Glossary
ASVAB glossary
The words these questions assume you already know, in plain language. Each term lists the guides that teach it, and each guide links to the term where it first appears.
- alternating currentAlternating current (AC) reverses direction at a regular frequency — 60 cycles per second in North America — and is the current a wall outlet supplies.
- alternatorThe alternator is the belt-driven generator that makes electricity while the engine runs, using it to charge the battery and run the lights, ignition and electronics.
- aspect ratioA tire's aspect ratio is the sidewall height written as a percentage of the tire's width, so 65 in P215/65R15 means 65 per cent of 215 mm, not 65 mm.
- ball-peen hammerA ball-peen hammer has a flat face on one end and a rounded ball head on the other. It is a metalworking hammer: the flat face drives punches and chisels, and the ball peens metal.
- brake fluidBrake fluid is the liquid that carries hydraulic pressure from the master cylinder to a caliper at each wheel, and it is changed on time because it takes on water.
- camshaftThe camshaft is the rotating shaft whose egg-shaped lobes open and close the engine's valves, letting the air-fuel mixture in and the exhaust gases out at the right moments.
- capacitorA capacitor is a component of two plates separated by an insulator that stores charge and gives it back, so it blocks steady current and passes a changing signal.
- catalytic converterA catalytic converter is the exhaust part that cleans the exhaust gases. Hot gases pass over a catalyst coated honeycomb that turns carbon monoxide and other pollutants into less harmful ones.
- cell membraneThe cell membrane is the thin outer boundary of a cell. It holds the cell together and controls what passes in and out; plant cells also have a rigid cell wall outside it.
- charcoal canisterThe charcoal canister traps fuel vapor from the tank on activated charcoal instead of letting it escape, and holds it until the engine can purge the canister and burn it.
- check-engine lightThe check-engine light means the computer has found a fault and stored a code, so it is a drive-to-a-scan-tool warning rather than a stop-right-now one.
- chemical changeA chemical change makes a new substance — rusting, burning, cooking and reactions with an acid. The evidence is a change that is hard to reverse: a new color, a gas, a solid or heat.
- circular sawA circular saw is a power saw with a toothed disc that spins up through the base plate. The blade is set to clear the material, and the saw is pushed forward through the cut.
- circumferenceThe circumference is the distance around a circle, equal to π times the diameter, or 2πr. Use 3.14 for π unless the question says otherwise.
- claw hammerA claw hammer has a flat face for driving nails and a curved two-pronged claw for pulling them out. The claw works as a lever to multiply your pull.
- clutchThe clutch connects and disconnects the engine from the transmission. Press the pedal and the friction surfaces separate, so the engine can keep turning while gears are changed.
- compression strokeThe compression stroke is the second of the four strokes in a four-stroke engine: the piston rises with the valves closed and squeezes the air-fuel mixture into a smaller space.
- conductorA conductor is a material that lets electric charge flow through it freely. Copper and aluminum do it best, which is why wires and cables are made of copper.
- convectionConvection moves heat by moving the heated material itself: warm fluid or air expands, rises because it is less dense, cools, and sinks, setting up a circulating current.
- crankshaftThe crankshaft turns the pistons' up-and-down motion into rotation. Each piston's connecting rod rides a journal on the crank, and the spinning shaft is the engine's output.
- densityDensity is how much mass is packed into a given volume — mass divided by volume. An object floats in water when its density is lower than water's and sinks when it is higher.
- dial caliperA dial caliper measures outside, inside and depth dimensions, and reads them on a round dial instead of a ruler — commonly to a thousandth of an inch.
- differentialA differential is the drivetrain gear set that sends power to both driven wheels while letting them turn at different speeds, so the outer wheel can turn faster in a turn.
- diodeA diode is a semiconductor one-way valve: current passes in one direction only, and its symbol is a triangle pointing into a bar.
- direct currentDirect current (DC) is current that flows in one direction only, at a steady value. Batteries, solar panels and the electronics inside a device all run on it.
- distractorA distractor is a wrong answer choice written to look plausible. ASVAB distractors are near misses — related meanings, wrong parts of speech, or a straight reversal — not nonsense.
- EGR valveThe EGR valve sends a small, metered amount of exhaust gas back into the intake, which cools the burn and holds down the nitrogen oxides an engine makes when it runs hot.
- exponentAn exponent tells you how many times to multiply a number by itself: 2 to the third power means 2 × 2 × 2. It is shorthand for repeated multiplication.
- flat washerA flat washer is a thin disc that sits under a nut or bolt head and spreads the fastener's load over a wider area, so the surface is not crushed and the hole is not enlarged.
- food chainA food chain is the path energy takes through an ecosystem: producers such as plants make food from sunlight, consumers eat them, and each step passes on less energy than the last.
- frictionFriction is the force that opposes motion when two surfaces are in contact. It turns movement into heat, and it depends on the surfaces and how hard they are pressed together.
- fulcrumThe fulcrum is the fixed point a lever turns about — the pivot. Where it sits sets how much force the lever needs: closer to the load means an easier lift.
- gear ratioA gear ratio compares the teeth on two meshing gears. Divide driven teeth by driving teeth: the gear with more teeth turns slower and with more force.
- GFCIA GFCI is a ground fault circuit interrupter: an outlet or breaker that compares the current going out with the current coming back, and cuts the power the instant the two differ.
- greatest common factorThe greatest common factor of two numbers is the largest number that divides both evenly. It is used to simplify a fraction to lowest terms.
- hacksawA hacksaw is a fine-toothed saw with a narrow blade held under tension in a frame. It is the tool for cutting metal — pipe, rod, angle iron and bolts.
- hydraulicsHydraulics uses a liquid under pressure to transmit force. Because liquids barely compress, a small push on a small piston produces a much larger force on a big one.
- inclined planeAn inclined plane is a sloping surface used to raise a load gradually instead of lifting it straight up. A gentle long ramp needs less force than a steep, short one.
- inertiaInertia is an object's resistance to any change in its motion; it grows with mass, so the heavier object is the harder one to start, stop or turn.
- inferenceAn inference is a conclusion the passage supports without stating it: one step from the words on the page, not an added fact and not your own opinion.
- insulatorAn insulator is a material that does not let charge flow — rubber, glass, plastic, dry wood. It is why a wire is wrapped and a tool handle is covered.
- integerAn integer is a whole number — positive, negative or zero: …, −2, −1, 0, 1, 2, …. Nothing with a fractional part is one, so 3.5 is not an integer and neither is 1/2.
- jack standA jack stand is the rigid support that holds a lifted car up, because a jack is for lifting and nothing may be under a car a jack alone is holding.
- kerfThe kerf is the width of the slot a saw blade cuts, set by its bent teeth; it is wider than the blade's plate, so the cut removes material you have to allow for.
- kickbackKickback is a power saw throwing the work — or itself — back at the operator, and it happens when the blade grabs the material instead of cutting it cleanly.
- kinetic energyKinetic energy is the energy of motion — the energy an object has because it is moving. It grows with the object's mass, but with the square of its speed.
- least common multipleThe least common multiple of two numbers is the smallest number both divide into evenly. It is the common denominator when you add fractions.
- leverA lever is a rigid bar that turns about a pivot called a fulcrum. A long effort arm and a short load arm let it lift far more than the force you apply.
- lock washerA lock washer is a split or toothed washer that bites into the nut and the work and holds the fastener tight against vibration, so a bolt does not walk loose.
- main ideaThe main idea is the central claim a passage is built to support — what the author wants you to take away, and what the other sentences exist to prove.
- mass airflow sensorA mass airflow sensor sits in the intake and measures how much air is on its way into the engine, so the computer can add the matching amount of fuel.
- master cylinderThe master cylinder is the pump that turns the brake pedal's push into hydraulic pressure, forcing brake fluid down the lines to each wheel's brake.
- mechanical advantageMechanical advantage is how much a machine multiplies the force you apply: a lever, gear or pulley trades distance for force, so a small effort raises a large load.
- medianThe median is the middle value of a set of numbers once they are in order. Half the values lie below it, half above, and it is not moved much by an outlier.
- micrometerA micrometer is a precision measuring tool that closes a spindle onto a part and reads the gap on a scale, to the nearest thousandth of an inch.
- mitochondriaMitochondria are the cell structures that release the energy stored in food, which is why they are called the cell's powerhouses; a hard-working cell like a muscle cell is packed with them.
- modeThe mode is the value that appears most often in a set of numbers. A set may have one mode, several modes, or no mode if every value appears once.
- OBD-IIOBD-II is the standard under-dash diagnostic socket that lets a scan tool talk to the engine computer and read the fault codes it has stored.
- oil-pressure lightThe oil-pressure light warns that oil is not circulating under pressure, which is why it means stop the engine rather than wait and check the level later.
- order of operationsThe order of operations is the agreed sequence for evaluating an expression — parentheses, then exponents, then multiply and divide, then add and subtract, left to right within a step.
- oxygen sensorAn oxygen sensor sits in the exhaust and measures how much oxygen is left over after the burn, so the computer can tell whether the last mixture ran rich or lean and correct the next one.
- parallel circuitA parallel circuit offers several paths, so the same voltage sits across every branch and one failing branch leaves the others working. Total resistance falls as branches are added.
- part of speechA part of speech is the grammatical class a word belongs to — noun, pronoun, verb, adjective, adverb, preposition, conjunction or interjection — and it decides the job the word does.
- PCV valveThe PCV valve routes crankcase vapor — blow-by gas that gets past the piston rings — back into the intake so it is burned instead of vented into the air.
- percentA percent is a fraction out of 100: 15% means 15/100, or 0.15. To take a percent of a number, convert it to a decimal and multiply.
- perimeterThe perimeter is the distance all the way around a shape — add the lengths of every side. For a rectangle the formula is 2(length + width).
- periodic tableThe periodic table arranges the elements by atomic number in rows called periods and columns called groups; elements in the same group behave alike because they share outer electrons.
- pH scaleThe pH scale runs from 0 to 14 and measures how acidic or basic a solution is: below 7 is acidic, exactly 7 is neutral, and above 7 is basic, or alkaline.
- photosynthesisPhotosynthesis is how a plant uses light energy to turn carbon dioxide and water into sugar, releasing oxygen; respiration runs the reaction the other way.
- physical changeA physical change alters a substance's size, shape or state — melting, freezing, dissolving, tearing — without making a new substance. The material is the same before and after.
- pistonA piston is the close-fitting plug that slides up and down in an engine's cylinder. It receives the push of combustion and passes it to the crankshaft through the connecting rod.
- plumb bobA plumb bob is a pointed weight hung on a cord. Gravity pulls the cord straight down, and the line it makes — a plumb line — is used to check that something is vertical.
- plywoodPlywood is a sheet material of thin wood plies glued together with the grain of each layer at right angles to the next, which makes it strong both ways and stable in service.
- potential energyPotential energy is stored energy — the energy an object has because of its position or its condition, the way a raised weight or a stretched spring has energy waiting to be released.
- prefixA prefix is a word part added to the front of a root that changes its meaning — un-, re-, pre-, sub- and trans- among them. Learning a few unlocks dozens of words.
- prime numberA prime number has exactly two factors: 1 and itself. 2, 3, 5, 7 and 11 are prime; 1 is not, and 9 is not because 3 divides it.
- proportionA proportion states that two ratios are equal, such as 3/4 = 12/16. Solve it by cross-multiplying: multiply the two diagonals and set them equal.
- pulleyA pulley is a wheel with a grooved rim that carries a rope. A fixed pulley changes the direction of the pull; a movable pulley or block and tackle reduces the force needed.
- Pythagorean theoremThe Pythagorean theorem states that in a right triangle, a² + b² = c², where c is the hypotenuse. It finds a missing side whenever two are known.
- qualifierA qualifier is a word that limits a claim — all, some, most, only, never, always. Swapping one qualifier for another changes the meaning, and comprehension questions test exactly that.
- radiationRadiation is heat traveling as invisible electromagnetic waves. It needs no material to pass through, which is how the Sun's energy crosses empty space to warm the Earth.
- rangeThe range of a data set is the difference between its largest and smallest values — subtract the smallest from the largest. It is a measure of spread, not of center.
- ratioA ratio compares two quantities by division — 3 to 4, 3:4 and 3/4 are the same ratio. It says how many of one thing there are for each of the other, not how many in total.
- resistanceResistance is how much a material opposes the flow of current, measured in ohms. Rearranged from Ohm's law, R = V ÷ I: the more resistance, the less current flows.
- scopeScope is how much a statement claims — which things it covers and how much of them. A choice that widens or narrows the passage's scope is wrong even when its topic is right.
- series circuitA series circuit has one path, so the same current passes through every component in turn. The voltage is divided among them, and one break stops the whole circuit.
- slopeSlope is the steepness of a line: rise over run, or the change in y divided by the change in x. Two points (x₁,y₁) and (x₂,y₂) give (y₂−y₁)/(x₂−x₁).
- square rootA square root is the number that, multiplied by itself, gives the value you started with: the square root of 49 is 7, because 7 × 7 = 49.
- states of matterThe states of matter are solid, liquid and gas: a solid holds its own shape and volume, a liquid holds its volume but takes the shape of its container, and a gas holds neither.
- suffixA suffix is a word part added to the end of a root. It can change the meaning and, unlike a prefix, it usually changes the word's part of speech.
- synonymA synonym is a word that means nearly the same as another. ASVAB Word Knowledge asks for the synonym in some questions and the opposite in the others.
- tapA tap is a cutting tool that cuts a screw thread inside a drilled hole so a bolt can be threaded into it; a die cuts a thread on the outside of a rod.
- torqueTorque is a turning force — a force applied at a distance from the axis it turns — measured in pound-feet, and a torque wrench tightens a fastener to a set value.
- torque wrenchA torque wrench tightens a fastener to a measured amount of turning force, clicking or reading a scale at the value it was set to, instead of stopping when the bolt feels tight.
- transformerA transformer is two coils sharing a core; it changes alternating voltage by the ratio of turns between them — more turns on the secondary steps the voltage up, fewer steps it down.
- transmissionThe transmission is the gearbox between the engine and the wheels. It matches the engine's narrow speed range to the wide range the vehicle needs, trading revolutions for torque.
- try squareA try square is an L-shaped tool with a thick stock and a thin steel blade set at exactly 90 degrees. It marks and checks square corners and straight edges.
- turbochargerA turbocharger uses the engine's exhaust to spin a turbine that drives a compressor, forcing more air into the cylinders so more fuel can be burned and more power made from the same engine.
- viscosityViscosity is a fluid's resistance to flow — how thick it is. Motor oil is graded for it, so a 5W-30 oil describes how it behaves cold and how it behaves hot.
- voltageVoltage is electrical pressure — the push that drives current around a circuit. It is measured in volts and is written as V in Ohm's law, V = I × R.
- water cycleThe water cycle is the endless movement of water between the ocean, the air and the land — evaporation, condensation, precipitation, and runoff or infiltration back to the sea.
- wedgeA wedge is two inclined planes set back to back, driven into a material to split it or hold it apart. The thinner it is, the less force it takes to drive in.
- wheel and axleA wheel and axle is a large wheel fixed to a smaller shaft so both turn together. Effort on the wheel gives a greater force at the axle.
- word rootA word root is the part of a word carrying its core meaning, with prefixes and suffixes built onto it. Most English roots come from Latin or Greek, and one root usually builds a whole family.