Ground - refers to a point of zero voltage or potential.
Ground Loop - An unwanted current in a conductor connecting two points which supposed to be at the same potential, i.e. ground, but are actually at different potentials. This causes noise (typically at 60Hz) within an audio or video system.
Group Delay - The group delay of a filter is a measurement of the average delay of the filter as a function of frequency. It is the negative first derivative of a filter's phase response. It also can refer to the delay of a speaker from the listening position.
Harmonic - the multiple frequencies of a given sound, created by the interaction of signal waveforms.
Harmonic Distortion - harmonics artificially added by an electrical circuit or speaker, and are generally undesirable. It is expressed as a percentage of the original signal.
HDMI - A digital audio connection which is capable of carrying DRM-protected lossless 7.1 audio and HD video over a single jacketed cable. While it provides some strain relief, this now-dominant format isn't exactly the cat's meow in terms of the perfect connector, but it looks to be here to stay. HDMI 1.3a is the latest iteration as of mid-2007 and supports Dolby Digital Plus, Dolby TrueHD, DTS-HD and DTS-HD Master Audio, as well as all legacy digital audio formats. 1080p over HDMI can currently be sent about ~30-40 feet before requiring a DC-powered cable EQ or relay.
Hertz (Hz) - a measurement of the frequency of sound vibration. One hertz is equal to one cycle per second. The hertz is named for H.R. Hertz, a German physicist.
High-pass Filter - an electric circuit that passes high frequencies but blocks low ones by acting as a large impedance to those frequencies.
Hiss - background audio noise that sounds like a Rattler snake.
Home Theater - an audio system designed to reproduce the theater sound experience while viewing movies in the home. A basic system usually consists of a Dolby Prologic Decoder, 5 speakers and a subwoofer. More advanced systems incorporate Dolby Digital/DTS and other discrete 5.1 channel surround formats.
Horn - a speaker design using its own funnel shaped conduit to amplify, disperse, or modify the sounds generated by the internal diaphragm of the speaker.
HQV (Hollywood Quality Video) - Refers to a video processing technology by Silicon Optix which provides scaling, de-interlacing and noise reduction (among other things) to standard and high definition video sources. Silicon Optix also puts out a handy HQV Benchmark DVD (now available in HD DVD and BD formats) to test displays and source components.
Hum - audio noise that has a steady low frequency pitch, often caused by ground loops.