Yesterday I posted about bike "saddles," preferring to use that term rather than "seat" for reasons of custom and, as a matter of fact, clarity (a "seat" implies you sit on it, legs in front like a chair or bench, a "saddle" is something you straddle like the thing on a bicycle or a horse).
But while you sit on a saddle, the saddle itself sits atop a seatpost, which made me realize that there are a ton of terms and jargon used in the bike industry that probably make no sense to anyone who hasn't been behind a shop counter. While I try to avoid using any more bike-specific jargon, there's a few terms to know that are helpful, not only to follow along on mine or other bike-related pages on the internet, but also to be able to communicate clearly with your bike shop.
I'm not going to to try to put together a comprehensive bicycle glossary, but give you a few of the most useful terms. For something more completist, see Sheldon Brown's work here.
By Category, rather than by alphabet:
Road Bike: A bicycle made for pavement riding. Built for light weight and aerodynamic efficiency, with narrow tires, a leaned-forward riding and no shock absorbers. Usually has drop handlebars and integrated brake-shift levers on newer models.
Mountain Bike: A bicycle made for off road use. Features fat tires with tread meant to grip on loose surfaces, and lower gearing than a road bike. Usually has at least a front shock-absorber, may also have one for the rear wheel.
Hybrid Bike: Made to be something between a road and mountain bike, often has straight handlebars and gearing higher than a mountain bike, but usually lower than a road bike. The tires will be fatter than most road bikes, but not have the tread design of an aggressive off-road machine.
Sport-Comfort Bike: Industry term for a type of hybrid bike that has mountain-bike sized (26") wheels. Often looks like a mountain bike, but with much higher handlebars, a cushier seat and smoother tire tread.
Flat-Bar Road Bike/Fitness Bike: A type of hybrid that is close to a road bike in geometry, gearing and tire size, but has straight handlebars and a more upright riding posture. Usually less expensive than a road bike due to simpler shifting mechanisms.
City Bike: Any bike designed for urban riding, usually some sort of hybrid.
Cruiser: A bike with very fat, low-pressure tires, a wide seat, dramatically swept handlebars and a very upright sitting position. Comfortable for short rides, but not ideal for getting up hills. Often referred to as a "beach cruiser" because of their popularity in flat, coastal areas and on boardwalks.
Touring Bike: A bike made for long-distance rides from one point to another, usually a variation on a road bike, but sometimes a hybrid or mountain bike. May be set up to carry heavy loads including camping gear, but some carry little more than a change of clothes and snacks.
Stem: The thing that attaches the handlebars to the bicycle. Comes in two flavors, Threadless (clamps onto the outside of the steering tube) and Quill (slides into the steering tube and fastens with an expander bolt).
Drop Handlebars: Road and racing bike handlebars that curve downward in a "ram's horn" shape.
Flat Bars: Straight handlebars
Riser Bars: Handlebars whose shape curves upwards from where they're clamped into the stem.
Bar ends: things that clamp onto the end of flat bars to give you an extra hand position
Aero Bars: extensions that allow you to lean forward with your elbows and forearms resting on the handlebars. Done for aerodynamics, not for comfort.
Grips: The coverings (usually rubber) that go on the handlebars to make them more comfortable for your hands
Bar Tape: a padded tape that wraps around drop bars to provide a gripping surface and some cushioning.
Brake Lever: The thing on the handlebar that you move to activate a brake
Coaster Brake: A type of brake contained in the rear hub of the bike, activated by turning the pedals backwards. Common on cruiser bikes and some city bikes.
Caliper Brake: A "U" shaped brake, common on road bikes, that attaches to the bicycle with a single bolt and grabs the rim of the wheel.
Cantiliver brake: A type of rim brake that attaches with two bolts, one on either side of the bicycle frame or fork. Comes in two flavors, Centerpull (a cable straddles the two brake arms, and another cable pulls upwards on it to pinch them together) or Linear Pull, aka "V-Brake" (the brake cable runs through the side of one arm and attaches to the other).
Disc Brake: A metal disc attaches to the center of the wheel. Brake calipers grab the disc rather than the wheel itself. Similar to brakes on cars or motorcycles, just smaller and more lightweight. Two flavors again, mechanical (a cable pulls a lever on the brake which moves the calipers) or hydraulic (uses special brake lines full of fluid, much like a car).
Brake cable: The cables that connect the brake to the brake lever. Usually made of a wound steel wire running through some sort of flexible housing made of metal coated in plastic. The cable and the housing are sometimes referred to as "inner and outer cable". Housing may be "full" (runs from the lever to the brake, covering the inner cable all the way) or interrupted (it ends in special brackets on the frame of the bike, leaving sections of inner cable exposed).
Brake Pads/Brake Shoes: The part of the brake, usually made of some sort of rubber compound, that grips the wheel to slow or stop it. Because of the friction involved, these are the quickest-wearing part of the bike. Easily replaced, and usually inexpensive, but you need to make sure you get the right style of pad for the type of brake you have (best bet is to bring the old, worn-out pad with you to the shop).
Wheel: The whole wheel, all the parts put together
Tire: The rubber part part that touches the ground. Will have different tread designs depending on use. Comes in many sizes. The thickness of tires can vary, but the inside diameter must match the wheel on which it is to be mounted. Making sure you have the right tire size can be really difficult, especially on older bikes, as there are a wide array of them, and they weren't well standardized till recent decades.
Tube/inner tube: The balloon-like thing inside the tire that holds the air. Usually, flats mean replacing the inner tube. Inner tubes are sized to match tires. Has a valve to put air in, which projects through a hole in the wheel.
Hub: The center of the wheel, which rotates around the axle.
Axle: The rod that runs through the center of the wheel and attaches it to the bicycle. The part of the wheel that doesn't spin. May use nuts or a quick-release mechanism to make it fit tightly.
Rim: The outer edge of the wheel, on which the tire mounts. Usually aluminum or steel.
Spokes: The rods that connect the hub to the rim. Tension on these keeps the wheel even, and minor irregularities can be worked out by adjusting the tension on specific spokes. The little widget that threads on one end of the spoke to attach to the rim and adjust tension is called the nipple.
Pedals: The little platforms on which you rest your feet
Crank: The assembly which transfers the movement of the pedals to the bike. Made up of two crankarms, a spindle to connect them and from one to three toothed sprockets called chainrings
Bottom Bracket: The bearing assembly attached to the bottom of the bicycle which allow the crank to rotate. The crank spindle is often attached to the bottom bracket, but not always.
Chain: the chain. Varies in width depending on how many gears are in the rear cluster. The wrong chain can lead to jammed drivetrains.
Freehweel: A type of gear cluster which screws directly onto the hub. The ratchet mechanism is contained in the freewheel itself, rather than part of the rear hub.
Cassette: A type of gear cluster which has no ratchet mechnism, attaches to a "freehub" rear hub, where the ratcheting mechanism is contained within the hub body itself.
Derailleur: The device which moves the chain from one cog to another. Front derailleurs mount by the cranks and move the chain from one chainring to the others, rear derailleurs hang below the rear axle and move the chain around the cassette or freewheel.
Shifter: The gadget on the handlebars (or sometimes, on older bikes, on the frame or stem) that controls the derailleurs by pulling on a cable. Cables are similar to brake cables above, but have different ends.
X-Speeds: When speaking about how many "speeds" a bike has, we refer to how many gears are on the rear cluster, because this affects shifter and chain choice. Bikes can have between one and 11 cogs in the rear, therefore in modern terminology, a "ten-speed" bike is a bike with ten rear cogs, and one, two or three chainrings (10-30 possible gear combinations). Front choices are called single, double, or triple, depending on how many chainrings there are. Therefore, a bike with two chainrings and nine cogs in the back would be referred to as a "9-speed double."
This may seem counter-intuitive, but it makes finding parts and repairs a lot clearer (for example, if you say you have an "18-speed" does that mean you have a bike like that above or one with six rear cogs and three chainrings? Both exist, but the parts are not compatible at all). Most entry-level mountain bikes are 7-Speed triples.
Internal Gears/Gearhubs: The gearing mechanisms are all contained within the rear hub, withe no derailleurs. Between two and 14 gears are possible, and infinitely variable gearhubs exist.
Frame: The skeleton of the bike. Often diamond shaped, but there are variations.
Fork: The part of the bike that holds the front wheel. Consists of a steer tube (central part which goes through the frame to connect to the stem), crown (part where the fork splits), legs or blades (go on either side of the wheel) and dropouts (fittings where the axles attach. Mountain bike forks often have spring-loaded legs, in which case it's called a "suspension fork." Suspension forks are becoming common on hybrid and comfort bikes as well.
Head Tube: The tube at the front of the bike through which the fork's steer tube runs. The bearings in the head tube, which allow steering, are referred to as the "headset".
Top Tube: The tube at the top of the bike. May be parallel to the ground or angled.
Down Tube: The tube that runs down from the head tube to the bottom bracket shell
Bottom Bracket Shell: The tube, set perpendicular to the other tubing, through which the crank bearings run.
Seat Tube: The tube connecting the bottom bracket shell to the top tube. The seatpost slides in here, and is secured by a clamp just above the top tube (called, appropriately enough, the "seat clamp"). Often, when the size of a bike is given in inches or centimeters, it refers to the lengthy of the seat tube. Longer seat tube=taller bike.
Seat stays: The twin tubes that run from near the top of the seat tube to the rear axle. May be two completely seperate tubes or joined in a "Y" shape before meeting the seat tube.
Chain stays: The tubes that run from the bottom bracket shell to the rear axle.
Dropouts: The place where the stays connect, containing fittings to attach the rear axle.
Bosses: any fittings attached to the frame to attach racks, brakes, water bottles or other accessories. Brake bosses usually look like posts sticking out of the frame or fork, whereas water bottle bosses are threaded nuts set into holes in the frame tube.
Hanger: fitting which attaches the rear derailleur to the frame. May be replaceable in case of damage.
Commuter: Sometimes used strictly to refer to someone who bikes to work, but as a broader term meaning anyone who uses as bike as transportation rather than just for sport. AKA "Transportation Cyclist" or "Utility Cyclist."
Racer: Someone who rides primarily to race, or to train for racing.
Fitness Cyclist: Someone who rides strictly for exercise.
Recreational Cyclist/ Family Cyclist: Someone who rides for fun, without specific fitness or transportation goals (most cyclists from other categories also ride recreationally).
Touring: Riding your bike to a destination at which you intend to stay overnight. Three-major categories of touring are "Loaded" (carry everything you need, including food and camping gear) "Credit Card" (carry just clothing and minimal gear, stay at hotels, B&Bs or friends' houses) and "Supported" (ride from site to site, but have someone else carry your gear, usually a tour company with a van).
MUP/MUT: Multi-Use Path/Trail, a place where cars aren't allowed, but bikes, walkers, joggers, etc are, as opposed to a dedicated bike path.
JRA: A bicycle-shop acronym for "Just Riding Along." Often used descriptively as in "bike makes a clicking noise JRA, check shifting," but sometimes used derisively when shop employees suspect a customer is lying to avoid admitting responsibility for damage, as in "customer says he was JRA when the rear derailleur spontaneously broke. Scuffed paint, gravel and ripped bar tape from apparently crashing the bike must have nothing to do with it."
Bummel: A somewhat-uncommon term probably used mostly just by me. Taken from Jerome K. Jerome's humorous cyclo-touring book "Three Men on the Bummel." It means a ride with no particular goal or destination, but a time limit. For example, if you have Sunday off, and if you hop on your bike and ride around all day just for the hell of it, you can be said to be "on the bummel." The same can be said if you have a few days off and go on an overnight trip, stopping when you see a likely motel or campground, not following a strictly planned route, but keeping in mind you've got to get to work on Monday. My favorite type of recreational riding, especially for day trips.