Acorn nut: a nut with a rounded end usually filled with grit from the shop floor and residing under a cabinet after falling and bouncing there 10 years ago.
Adjustable Cup: the side of the three-piece bottom bracket that usually self-loosens and rattles 35 miles from home.
Ærodynamic: a Raleigh DL-1 with a 6 foot tall rider on it, going uphill.
Aftermarket: a set of Wald fenders that weigh 48 ounces and rattle like paint cans filled with quarters.
Alignment: eye-balling a frame and hitting it with a hammer until it looks to be within 6 inches of straight.
Allen Wrench: a bent key with a hex-shaped profile usually stepped on when wearing no shoes.
Alloy: a mix of unknown metals forming a single, also-unknown metal that usually forms the basis of Wal-Mart soup pots.
Alpine gearing: any gearing, including single speed beach cruiser gearing, that a person uses to climb any sort of hill and then brag about it on a bike-related internet forum.
Alternate Cable Routing: routing a cable around the wrong side of a bike and then selling it as 'innovation'.
Aluminum: what cans and cracked frames are made of.
Anti-rotation Washer: a washer beaten into place with a 5-pound hammer and then glued where it stops.
Ass: when on a bike, this is any person who passes you on another bike, while he is driving a car, or especially while he is walking.
Ashtabula crank: a piece of steel used in medieval years as a weapon and later bent into the shape of crank arms.
Autoshifting: a derailleur with a cable tightened to the max using vise grip pliers.
Axle: the bent and/or cracked piece of steel at the center of a wheel stripped of its threads with a torque wrench.