AF — Audio Frequency
The band of frequencies (approximately 20 Hz to 20 kHz) that, when transmitted as acoustic waves, can be heard by the normal human ear.

AM/FM
The two commercial radio systems in use in the US. Amplitude Modulation stations can be heard at great distances — especially at night, but are subject to interference and low fidelity. Frequency Modulated signals can only travel in a line of sight manner (generally 30-40 miles) but offer higher fidelity.

AM/FM Presets
Allow you to store your favorite stations in memory for recall at the touch of a button.

Amplifier Power
Measured in watts, amplifier power is used to drive speakers. More power generally provides a clearer sound as well as an increase in loudness. However, other features can influence clarity in addition to just power.

AMPS — Advanced Mobile Phone System
Analog transmission technology that operates in the 800MHz frequency band.

Analog
A signal that represents data in continuously variable physical quantities, whereas digital data is represented in discrete units (binary digits 0 and 1). An analog sound wave signal is continuous. When converted to digital it is a sampling of intervals. Analog information can be converted to digital and visa versa.

ANSI Lumens
ANSI is an acronym for the American National Standards Institute, an organizational body that creates standards for the computer industry. Lumens is a standardized method of measuring the average brightness of projection devices. The brighter the image, the more heat generated and power consumed.

Aspect Ratio
The physical length of the vertical axis divided by that of the horizontal axis, ratio between the width of the picture and the height of the picture. Letterbox format has an aspect ratio of 16:9.

A/V Inputs (composite)
These are the standard jacks used to hook up audio and video components to each other. Input jacks allow the signals to be received from other components; having more inputs than you need right now is helpful for future system expansion needs.