Glossary

A

Add-a-leaf: An add-a-leaf is an extra steel leaf inserted into an existing leaf spring pack to raise the back of a truck and stiffen it for load, as a cheap alternative to replacing the pack.
Airing down: Airing down is letting air out of your tires before a trail to lengthen the tire's footprint on the ground, which trades better traction and a softer ride for a lower highway speed limit and, taken far enough, a real risk of the tire popping off the rim.
Amber light: Amber light is off-road lighting in the yellow part of the spectrum, and what the manufacturers who sell it claim for it is less glare back from dust and fog, not better penetration through them.
Approach angle: Approach angle is the steepest ramp a vehicle can drive onto without anything at the front touching first, measured between the ground and a line drawn from the front tire's contact patch up to the lowest point ahead of it.

B

Backscatter: Backscatter is light from your own lamps hitting airborne dust, fog or snow and bouncing back toward you, and it is why a badly placed light can leave you seeing less than you would with none.
Beadlock wheel: A beadlock wheel clamps the tire's bead to the rim mechanically instead of relying on air pressure alone, which lets a tire run at very low pressure off-road without the bead unseating, and most designs built that way are not legal to drive on a public road.
Beam cutoff: A beam cutoff is a sharp upper edge to a light's beam, above which it throws almost nothing, and it is the optical feature that makes a wide beam usable when the air is full of dust, fog or snow.
Beam distance: Beam distance is how far from a lamp its beam has faded to whatever threshold of light the maker counts as useful, and the flashlight industry's convention puts that threshold at 0.25 lux, which works out as twice the square root of the lamp's peak candela.
Breakover angle: Breakover angle is the sharpest ridge a vehicle can drive over without grounding out in the middle, measured between the two tire contact patches and the lowest point of the chassis between them.

C

Candela: The candela is the SI base unit of luminous intensity, meaning how much light a source sends in one particular direction, and it is the number that decides how far a light actually reaches.
Center of gravity: A vehicle's center of gravity is the single point its whole weight acts through, and how high that point sits above the ground is the largest factor in whether the vehicle leans, tips or rolls.
Color temperature: Color temperature is the number in kelvin that says whether a white light looks warm and yellowish or cool and bluish, and it describes appearance only, not how bright a light is or how far it reaches.
Combo beam: A combo beam is one lamp or bar carrying two different optics at once, usually a narrow spot for distance blended with a wider pattern for the near ground, so a single housing covers both jobs without doing either at full strength.
Cornering light: A cornering light is an auxiliary light aimed out to the side rather than straight ahead, so it fills the space either side of the trail that headlights leave dark.
Curb weight: Curb weight is what a vehicle weighs ready to drive but unloaded, fuel, oil and coolant at capacity with a full tank, nobody and nothing aboard, and it is the number subtracted from GVWR to get payload.

D

Departure angle: Departure angle is the steepest slope a vehicle can back down or drive off without dragging its tail, measured between the ground and a line from the rear tire's contact patch to the lowest point behind it.
Ditch lights: Ditch lights are auxiliary lights mounted at the hood corners or the base of the A-pillars and aimed outward, so they light the verges, the ditch and the inside of a turn where your headlights do not reach.
Driving light: A driving light is an auxiliary lamp that adds reach to your high beams and is wired to work only with them, which makes it the lamp for fast open ground and the wrong lamp for fog, corners or working around the truck.
Dual battery system: A dual battery system adds a second battery wired through an isolator or a DC-DC charger, so a fridge, lights or a winch can draw on the auxiliary battery without any risk of leaving the starting battery too flat to turn the engine over.

F

Flatbed tray: A flatbed tray is a flat open deck, usually aluminium, that replaces a pickup's factory bed completely, trading the tub's walls and wheel arches for a wider level floor with storage boxes hung underneath it.
Flood beam: A flood beam is a wide off-road light pattern, often forty degrees or more across, that fills the near ground and the sides at the cost of distance, and it belongs low because a wide beam lights a lot of air close to the vehicle.
Fog lamp: A fog lamp is a wide, low-mounted lamp with a sharp cutoff along the top of its beam, which lays light on the road surface and throws almost none above it, and it is that beam shape and its approval class that make it a fog lamp rather than the colour of the light.
Four-wheel drive: 4x4 means a vehicle with four wheels of which all four can be driven, the first number being the total wheels and the second how many receive engine power.

G

GAWR: GAWR is the maximum weight the manufacturer rates one axle to carry, measured where its tires meet the ground, and a truck loaded tail-heavy can be over its rear GAWR while still under its overall GVWR.
Gear ratio: A gear ratio, usually called the axle ratio in a truck, is how many times the driveshaft turns for one turn of the wheels, and a numerically higher ratio trades top speed for torque, which is what a low crawl ratio is built from by multiplying it with the transfer case and first gear.
Ground clearance: Ground clearance is the distance from the ground to the lowest fixed point under a vehicle, which means it is set by whatever hangs lowest rather than by how tall the tires are or how much lift is fitted.
GVWR: GVWR is the maximum loaded weight the manufacturer certifies a vehicle for, printed on a label in the driver's door jamb, and it covers the vehicle, everything bolted to it, everyone in it and everything packed in it.

H

Hawse fairlead: A hawse fairlead is a smooth aluminium block that guides a synthetic winch line onto the drum without letting it saw against the bumper, and it exists because synthetic rope does not need the rollers steel cable needs, and is damaged by them.
Hidden winch mount: A hidden winch mount is a bracket that carries a winch behind a vehicle's factory bumper instead of inside an aftermarket one, keeping the standard front end at the cost of approach angle and access.

I

Independent front suspension: Independent front suspension lets each front wheel move up and down on its own, which rides, steers and handles better on the road than a solid axle, at the cost of articulation, clearance under the front differential and some ultimate strength.

K

Kinetic recovery rope: A kinetic recovery rope is a nylon rope built to stretch under load, storing energy from a moving vehicle and releasing it to pull a stuck one free, which makes it a different tool from a tow strap and not a substitute for one.

L

Lift kit: A lift kit raises a vehicle's ride height, most often to clear bigger tires, either by replacing the suspension parts that space the axles from the frame, which genuinely gains clearance, or by inserting spacer blocks between the body and the frame, which raises the sheet metal without moving the axles at all.
Light bar: A light bar is a long housing holding a row of LED emitters, sold and mounted as one unit, and its shape is a packaging decision rather than an optical one.
Locking differential: A locking differential forces both wheels on an axle to turn at the same speed, so a wheel with grip keeps getting power even when the wheel on the other side is spinning in the air.
Lumen: A lumen is the SI unit of luminous flux, meaning the total amount of visible light a source puts out in all directions added together, which tells you how much light exists and nothing about where it goes.
Lux: A lux is one lumen falling on one square metre, so it measures light arriving on a surface rather than light leaving a source, and it is the unit behind the distance figures off-road lamps are advertised by, though makers differ over how much of it still counts.

O

Overlanding: Overlanding is vehicle-based travel where the journey itself is the point, the vehicle carries what you need to be self-sufficient, and the destination is usually somewhere with no services when you get there.

P

Payload: Payload is what is left of a vehicle's weight rating once the vehicle itself is on the scale, GVWR minus curb weight, and it has to cover the people, the fuel, the gear and every accessory bolted on since it left the factory.

R

Recovery point: A recovery point is a rated, frame-mounted attachment designed to take the shock load of a vehicle being pulled out, which is a different thing from a tie-down loop, and using the wrong one is the most common way recovery gear hurts somebody.
Rock lights: Rock lights are small lights bolted into the wheel wells or under the frame rails and aimed down, so a driver and a spotter can both see exactly where the tires, rocker panels and skid plates sit relative to the obstacle in front of them after dark.
Rock slider: A rock slider is a frame-mounted bar running along the side of a vehicle that can take the vehicle's full weight on an obstacle, protecting the rocker panel and giving you something to pivot on deliberately.
Rooftop tent: A rooftop tent is a tent built into a rack-mounted shell that folds out on top of a vehicle's roof, trading a ground tent's setup effort and low centre of gravity for a sleeping platform off the wet ground, at a real cost in weight and drag carried exactly where a vehicle can least afford them.

S

Scene lighting: Scene lighting is flood lighting mounted on the sides, rear or rack of a vehicle and aimed down at the ground around it, so a camp, a repair or a recovery can be worked in light while the vehicle stands still.
Skid plate: A skid plate is a panel of steel, aluminium or plastic bolted under a vehicle to protect the engine, transmission, transfer case or fuel tank from rocks, and to let the vehicle slide over an obstacle instead of catching on it.
Snatch block: A snatch block is a pulley you run a winch line through to double the pulling power, halve the speed, or change the direction of a pull, and despite the shared word it has nothing to do with a snatch strap.
Snorkel: A snorkel relocates a vehicle's engine air intake from low on the fender to roof height, mainly to keep trail dust out of the engine, with reaching deeper water crossings as the secondary reason most people say they fit one.
Soft shackle: A soft shackle is a loop of synthetic rope closed with a knot and an eye that does the job of a steel bow shackle at a fraction of the weight, and with far less to throw if something in the recovery fails.
Solid axle: A solid axle is a single rigid housing running the full width of the vehicle with a wheel fixed to each end, so the two wheels move and tilt together instead of independently, which trades on-road ride and steering precision for strength and off-road articulation.
Spot beam: A spot beam is a narrow off-road light pattern, typically under about ten degrees wide, that trades width for distance, and it is the only pattern with a good reason to be mounted high.
Spread beam: A spread beam is a wide off-road driving pattern shaped to push light sideways along the edges of the trail, and what separates it from a flood is where the light is aimed rather than how wide it is: a spread reaches out along the trail ahead, a flood fills the near ground around the vehicle.
Sway bar disconnect: A sway bar disconnect is a lever, pin or electronically actuated coupling that lets a driver unhook the front sway bar on demand, freeing the front wheels to articulate independently for more wheel travel on slow technical terrain, then reconnect it for stability once back on the road.

T

Tire placard: The tire placard is the yellow and white label in the driver's door jamb that states, in words federal law fixes, the most weight a vehicle's occupants and cargo may add together, along with its seating capacity and the factory tire sizes and cold inflation pressures.
Traction boards: Traction boards are stiff ramps with aggressive lugs that you wedge under a spinning tire to give it something to bite on, and they are the fastest self-recovery there is when the problem is grip rather than clearance.
Transfer case: A transfer case is the gearbox behind the transmission that sends engine power to the front axle as well as the rear, and usually offers a low range that multiplies torque for slow, difficult ground.

V

Veiling luminance: Veiling luminance is the even glow that scattered light lays over everything in your field of view, and it blinds you not by being bright but by shrinking the difference in brightness between an object and its background.

W

Winch: A winch is a motor-driven drum that pulls a vehicle out of trouble along a line anchored to something that is not moving, and its rated pull is the figure on the first wrap of line on the drum rather than the fifth.
Work light: A work light is a flood lamp for lighting the ground around a stopped vehicle while you work, and since nothing about its beam is shaped for oncoming eyes, it is a lamp to use parked and to switch off before moving.