Basketcase: A Basketcase is a pile of parts usually bought as a whole and supposedly from a single bike model. Basketcases are bought especially by motorcycle restorers to help finish out a restoration.

Belt Drive: Belt Drive is a method to transmit power from the transmission to the rear wheel of the motorcycle using a belt. The belt requires practically no maintenance. Harley-Davidson has used Belt-Drive systems on most of its motorcycles in recent years.

Bottom End: Bottom End refers to the bottom portion of a motorcycle engine including the crankshaft, connecting rods and bearings, primary chain, cam sprockets, seals, and other components that support delivering the power to the transmission and rear wheel of the machine.

Boxer: Refers to the BMW R-Series engine that has two horizontally opposed cylinders.

Bungee Cord: Bungee cords or nets are used to secure cargo hine.

Boxer: Refers to the BMW R-Series engine that has two horizontally opposed cylinders.

Bungee Cord: Bungee cords or nets are used to secure cargo to a bike. There are U-shaped hooks at the ends of the cords that fasten around various parts of the bike as anchors.

Cage: An automobile. (!!!)

Caliper: A Caliper is the non-rotating portion of the disc brake that contains the hydraulic components including the brake pads. The Caliper is positioned on both sides of the Rotor such that as the brakes are applied, the brake pads are pressed against both sides of the Rotor, thereby stopping the motorcycle.

Camshaft/Cams: A Camshaft is a shaft containing lobes (also called cams) which is synchronized with the crankshaft. Its function is to rotate and open and close the valves in the engine. Camshafts may be located on top of the heads of the engine (SOHC or DOHC) or near the crankshaft. When the camshaft is located near the crankshaft, its rotation causes its lobes to press on pushrods which extend to the top of the engine and connect to rocker arms which then open and close the valves. Harley-Davidson motorcycles are heavy users of the pushrod method of valve operation.

Centerstand: A Centerstand is a stand mounted under the motorcycle with a spring return. When the Centerstand is extended to the ground, it holds the motorcycle vertical with the rear wheel just off the ground. Such a stand is useful for leveling the bike and spinning the rear wheel to lub the chain (if used). It also makes a nice platform if you want to park your bike at the curb at a rally and watch all the other bikes go by.

Chain Drive: Chain Drive is a method to transmit power from the transmission to the rear wheel of the motorcycle using a chain. The chain is much like that on a bicycle requiring periodic lubrication -- a messy job.

Chaps: Most motorcycle riders like to have some protection on their legs while riding. A pair of leather chaps does the trick. Chaps usually have snaps near the ankles and a zipper down the legs. They're pulled around the waist like a belt and fastened. The backside is open.

Choke: The Choke is a device that restricts the air intake to result in a richer fuel mixture which assists in starting the engine. Most motorcycles have knobs or levers to pull out to decrease the air intake. After the engine has warmed up, the choke may be pushed back in. Warm motorcycle engines normally do not require choking to restart.

Chopper: A cruiser style bike that has a lot of the pieces of the bike "chopped off." The riders of the '60s did everything they could to customize their bikes and make them go faster. Thus, much of the existing bikes they bought were chopped off. The bikes in the movie "Easy Rider" are examples.

Clip-ons: Clip-Ons are special handlebars that clamp on. They provide a lower, more forward riding position. The forward shifting of the weight of the rider often results in better handling of the bike.

Clutch - Dry: A Dry Clutch is more like the clutch found on an automobile that separates the engine from the transmission. There is a dry connection between the engine and transmission.

Clutch - Wet: A Wet Clutch is one that contains many plates that are in the oil spray of the transmission and the oil gets between the plates. The plates on wet clutches have a tendency to stick together when the bike sits. So, when you start the bike in the morning, before you put it in first gear to move off, depress the clutch lever for about 30 seconds to allow the oil on the plates to drain off and the plates to separate. Otherwise, you'll get a decided clunk and slight movement forward when you put it in first.

Co-Rider: Motorcyclist riding on the back of a motorcycle behind the rider. The co-rider is an active participant and assists the rider during certain maneuvers. Could also be someone riding in a sidecar.

Colors: Many bikers/motorcyclists join motorcycle clubs. Usually these clubs have distinctive jackets. Also, clubs will issue club patches to display on the jackets. These patches and sometimes the jacket design itself are known as Colors. In certain motorcycle clubs there may be disputes over territory and the wording and arrangement of the various elements of the Colors. You may hear that certain establishments don't want any Colors displayed by bikers so that such disputes will not occur. The subject of Colors is a complex one and subject to considerable debate on motorcycle forums here on About and elsewhere.

Compression Ratio: Here's a definition from Motorcycles Forum moderator, Bill Wood: Think of Compression Ratio this way: When the piston is at the bottom of the cylinder, say you could pour 100cc of water into the sparkplug hole (both valves closed) and it would be full. When the piston is at the top of its stroke, you can only pour 10cc of water into the hole to fill it. The compression ratio would be 100 to 10 or 10 to 1. That's about as easy to understand as I can make it. Oops, forgot to say -- Higher compression ratios (in general) will let the engine make more power, require higher octane gas and be harder for the starter to turn over.

Contact Patch: The Contact Patch (CP) is the area on the ground where your motorcycle tire actually touches the road surface. This area can be very small and highlights the fact that there isn't much actual contact between your bike and the road.

Countersteer: A motorcycle turns left/right by slightly pushing the left/right handlebar. Push left, go left. Push right, go right. This is called countersteering.

Crash Bar: Many motorcycles have a Crash Bar or guard to protect the bike should it fall over. You'll have to look carefully on some bikes to see them and not all bikes are so equipped. Some models hide the protectors behind plastic covers. Look for extended areas on the bike where the guards may be hiding. For Newbies, a Crash Bar may be the only thing standing in the way of an expensive repair job that could cost you hundreds of dollars because of a simple tipover.

Crotch Rocket: A term some people use to describe a high-performance sportbike motorcycle.

Desmodromic: Desmodromic has to do with valve control in the engine. With desmodromic control, no return springs are used and the engine relies on compression to seat the valves. This is a design used previously by Mercedes and others but became an integral part of the Ducati motorcycle engine. It allowed for much higher rpm and horsepower and immediately proved itself in racing. See the book, Ducati, for illustrations of the Desmo valve control system and a description of its operating principles.

Disc Brake: A Disc Brake consists of both a rotating portion called the Rotor and a stationary portion called the Caliper. The Rotor is attached to the wheel of the motorcycle. The Caliper assembly parts work against the Rotor to apply pressure to it thereby stopping the wheel from turning. It's difficult to say precisely when the components of a disc brake should be replaced since so much depends on how the motorcyclist uses the brakes.

Displacement: Displacement is the volume displaced in the cylinders of an engine as the pistons move from their bottom position to their highest position in the cylinders. Displacement is measured in either cubic centimeters (CC) or cubic inches (CI).

DOT Helmet Rating: The Department of Transportation (DOT) rates motorcycle helmets. The rating is based on dropping the helmet containing a simulated head from a height of 10 feet. The "head" must receive no more than 400 Gs over a prescribed dwell time.

Drag Bars: Drag Bars are distinctive custom handlebars that are relatively straight and require a slight forward leaning to reach. The look is great but some complain about difficult low-speed handling. You may need long arms to have a successful experience using Drag Bars.

Dresser: Normally a large fully equipped bike with fairing, saddlebags, and a trunk.

Drum Brake: A Drum Brake is the older style of motorcycle brake. Most bikes use disc brakes these days. Drum brakes work by forcing brake shoes against the inside of a rotating drum that is part of the wheel. Many motorcycle trikes use drum brakes for rear brakes.

Engine Guards: see Crash bar

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source: http://motorcycles.about.com/cs/beginners/a/glossary0.htm