balance bike - a bicycle with no pedals or drivetrain, used by toddlers who are learning to balance.
bottom bracket - positioned at the bottom of the bike frame, connected to the crank arms.
brake levers - the hand-operated levers that control the brakes.
cassette - a cluster of cogs; found on multi-speed bikes.
cog - a rear sprocket.
chainguard - a protective sheath that covers the cog, chainring, and chain.
chainring - a front sprocket.
coaster hub - a hub with a built-in brake that can be used by pedaling backwards.
crank arms - the arms that the pedals attach to; connected to the bike frame at bottom bracket.
crankset - consisting of crank arms, bottom bracket, and chainring; the crankset uses the chain to convert pedaling into motion.
derailleur - the mechanism that moves the chain from one gear to another.
disc brakes - brakes which apply pressure to a rotor parallel to the wheel.
downtube - the downward slanting tube on a bike frame that runs from the headtube to the bottom bracket; where water bottle cages often go.
double-butted aluminum - aluminum that is doubly thick at all of the welded joints, but not in the center of the frame tubes.
drive side - the side of the bicycle with the chain and drivetrain; typically the right side.
drivetrain - all components related to the forward motion of the bike; including pedals, crank arms, chainring, chain, cog, and derailleur.
fork - often included as part of the frame, the fork holds the front wheel and is connected to the steerer tube.
frame - the main structure of the bike that all other bike components connect to.
freewheel - a rear wheel with a hub that freely allows backpedaling without braking.
gear - the combination of a certain cog and a certain chainring, which determines how easy or hard it is to pedal.
gear ratio - the number of revolutions the rear tire makes with one revolution of the pedals.
gearing - the arrangement of gears on a certain bicycle; the gear option(s) provided.
grips - the padded part of the handlebar intended for holding.