Imaging - it is the speaker’s ability to localize different instruments playing simultaneously.
Impedance - dependent on frequency, it is the AC equivalent of resistance in a DC circuit.
Inductance (L) - the capability of a coil to store energy in a magnetic field surrounding it. It produces impedance to an AC current (jwL) and acts as a short circuit to DC. Inductors are commonly used in audio as low pass crossovers.
Infinite Baffle - a flat surface that completely isolates the back wave of a driver from the front.
Infrasonic (Subsonic) Filter - a filter designed to remove extremely low frequency usually between 8-25Hz or lower, noise from the audio signal. Useful for Ported box designs.
Input - connection from signal source.
Isobarik Enclosure - enclosure where one woofer is buried in the enclosure and a second is mounted up against the first and wired in reverse polarity (there are other variations for Isobarik designs), but this one works best. This allows the effective Vas of both drivers working in this push-pull configuration to be half that of a single identical driver mounted normally. Very small enclosures may be constructed as a result, with increased power handling. Less efficient than other designs, but the push pull configuration greatly reduces second order harmonic distortion. The name Isobarik comes from a term that means "constant pressure".
Keystoning - The process by which a projector optically or digitally racks an image onto the screen in order to compensate for sub-optimal placement with relation to the projection screen. Vertical keystoning is often necessary and recommended for business projectors which are table-mounted, but is always avoided in home theater use due to the fact that even a minimum amount causes pixel blurring and loss of detail.
Lens Shift - The ability of a projector (typically LCD or LCoS, but now DLP as well) to move the entire optical system such that the image can be adjusted/centered, without keystoning, onto the screen from a less-than-ideal projector placement.
Letterbox - This typically refers to the presence of black bars on the top and bottom of a film when displayed on a 4:3 or 16:9 displays.
Low-Pass Filter - an electric circuit designed to pass only low frequencies and act as high impedance to frequencies out of the filters pass band.