Chainrings - The front cogs (either in a set of 2 or 3) fitted to the chainset. They increase in size from the inner to outer. For a mountain bike there are usually a set of three in order of 24, 34, 46 teeth. For a road bike, there are usually 2 chainrings: 39 and 52 teeth.
Crank - The metal arms that run from the pedal to the bottom bracket axle.
Pedal - These could be clipless, toe clips or the standard flat pedal.
Down Tube - The portion of theframe tube that runs from the bottom of the head tube to the bottom bracket.
Rim - The metal hoop of the wheel that the tire runs on.
Hub - The unit that holds the bearings for the wheel axle and supports the spokes at the center of the wheel.
Fork - The part of the bike that holds the front wheel, and turns to allow steering.
Brakes - These are what stop you. Mountain bike brakes are typically V-brakes. Other styles are cantilever and side pull brakes.
Headtube - The portion of the frame that contains the bearings in which the fork steerer tube rotates. The fork steerer tube is just the single upper tube coming from the top of the fork crown that goes through the headtube and to which the stem is attached.
Bar Ends - Extensions to your handlebars, that give you more powerful positions to climb with.
Stem - The welded tube assembly that connects the handlebar to the front fork's steerer tube. There are two types of stems: threadless & threaded. Threaded stems are the older style that is usually called a quill and it is L shaped. One end sticks down into the headtube and tightens in the fork's steerer tube. Threadless stems are a newer style that is meant to save a little weight (no other real advantage). In this case, the fork's steerer tube extends up and through the headtube to which the stem is then attached.
Top tube - The horizontal tube portion of the frame that runs from the top of the head tube to the top of the seat tube.
Front Derailleur - The gear mechanism that shifts the chain across the front chainrings. I have a page on adjusting the front derailleur.
Saddle - Your butt goes here. See pictures of my butt.
Seat Post - The removable tube that supports the saddle. You'll find seatposts made in steel, aluminum, titatinium and even carbon fiber. These different materials are meant to allow for a weight savings versus the steel seat post. But stiffness and shock absorbency are also qualities to look at.
Chainstays - The portion of the frame tubes that run from the bottom bracket shell to the rear dropout. It is usually made with the same material as the bike, as the frame is all one piece. But it is becoming a bit more popular to see carbon chainstays where these portions of the frame tube are made from carbon fiber and attached to the frame. This is meant to soften the ride.
Cassette - The name given to the set of cogs at the rear of the bike and driven by the chain. I have a page detailing the removal of the rear cassette
