Jargon Dictionary
Amp - See amplifier
Amplifier - A critical link in a quality audio system. This device takes low power RCA outputs from your head unit, and converts that to a higher power signal which can power one or more speakers. There are amplifiers built in to most head units and some speakers. When a speaker has an amp built in, it is referred to as a powered, or self-powered speaker.
Audiophile - A person described as an audiophile is someone who appreciates sound quality to a level beyond a normal person; you might compare an audiophile as a audio “junkie.” Generally these people have a obsessed with audio equipment, and spend more on new speakers and amplifiers than any sane person would. However, with all these cool gadgets it is much more fun to be insane. 
Bleeding edge - A one-up on an older phrase the cutting edge. The Bleeding Edge is of course described as being the same thing, but better. Generally, both phrases are used interchangeably.
Coaxial Speaker - This is a term for a speaker unit which has two speaker types packaged together, generally this will be a full-range or mid-range and a tweeter.
Cutting edge - This phrase used to described the very best product available, previous to the term the bleeding edge.
Deck - See Head Unit
Full Range Speaker - These speakers handle all frequencies of audio that you hear. Because of this however, they generally do not have the clarity that a dedicated sub-woofer or dedicated tweeter could give, with a few exceptions of high end speakers; generally you will want to avoid full range speakers.
Head Unit - The receiver of a car stereo. This is a combination of an amplifier, one or more tuner, and often a tape or CD player. It also is what controls what audio (or video) is played throughout your car. This unit, which sits on most every car’s dashboard is the device most people will simply call a radio, HU, Deck, Tape Player, CD Player, or many other terms.
Horn Tweeter - This is a high power tweeter generally used for PA systems, rarely seen in car audio. This specific implementation of a tweeter requires a outward facing cone, better known as a horn, similar to a blow horn, or bull horn. This horn gives an physical amplification of sound, but it is a bit too shrill for personal use.
HU - See Head Unit
Mid-Range Speaker - This is a speaker which is specially designed to handle most/all frequencies which are not covered by sub-woofers/tweeters.
One-up - A term used to describe being one better, for the sake of being one better. See bleeding edge for an example.
Reciever - See Head Unit
Speaker - Device which can be attached to the high power output of an amplifier to generate sounds.
Sub-woofer - Speaker which is specially designed to handle low frequency sounds (bass). This is the device you hear when the person next to you at a light has their trunk rattling, this side effect is from a poorly secured trunk or too large of a speaker. Contrary to popular belief it is possible to install a sub-woofer that does not attempt to overpower the rest of your sound system, or other neighboring vehicles; but that is less fun.
Triaxial Speaker - This is a term for a speaker unit which has three speaker types packaged together, generally this will be a woofer, a mid range and a tweeter.
Tweeter - This is a speaker which has been specially designed to carry high frequency sounds (some parts of some voices, as well as symbols, and other high pitched instruments and noises.) For high powered usage, there is a “horn tweeter” which acts like a tweeter, but is placed at the mouth of a horn which amplifies the sound greatly.
