Car Audio Terminology

Head Unit- The head unit is the centerpiece of the car's sound system, typically located in the center of the dashboard. Head units give the user control over the vehicle's entertainment media: AM/FM radio, satellite radio, CDs, cassette tapes (although these are now uncommon), MP3, GPS navigation, Blue tooth, etc. A head unit is also known as a receiver.

Subwoofer- A subwoofer is a woofer, or a complete loudspeaker dedicated to the reproduction of bass audio frequencies. Subwoofers, also known as "subs", are used to augment the low frequency performance of main loudspeakers. Subwoofers are constructed by mounting one or more woofers typically between 8" and 21" in diameter in a well-braced wood or plastic cabinet. Passive subwoofers have a subwoofer driver and enclosure; active subwoofers have a built-in amplifier.

Amplifier- Generally, an amplifier or simply amp, is any device that changes, usually increases, the amplitude of a signal. The "signal" is usually voltage or current. Amplifiers are made in either mono channel, 2 channel, or multi-channel configurations to allow you to increase the signal to more than one audio component.
Capacitor- Car audio capacitors are basically power storage's in the car. These capacitors accumulate that power which is essential for the amplifier to produce great sounds. This power is released when the demand for power exceeds the supply capacity of the power system of the car. You can hear the booming bass sounds and songs with that much needed punch only because of audio capacitors. Car audio capacitors are also known as stiffening capacitors.

Crossover- Audio crossovers are a class of electronic filters designed specifically for use in audio applications, especially hi-fi. Commonly used loudspeaker drivers are incapable of covering the entire audio spectrum with acceptable loudness and lack of distortion by themselves. Thus, crossovers serve the purpose of splitting the audio signal into separate frequency bands which can be handled by individual loudspeaker drivers optimized for those bands.

Tweeter- A small loudspeaker designed to reproduce high-pitched sounds in a high-fidelity audio system. A tweeter is generally capable of producing high frequencies from around 2,000 hertz to 20,000 hertz (20,000 Hz is generally considered to be the upper limit of the human ear).
Blue tooth- Simply put, blue tooth technology allows you to wire-lessly stream digital music from almost any audio player to another. Used mostly by more experienced and advanced car audio users.