Short for panorama. (1) (noun) Refers to the left-right placement of a sound.
(2) (verb) Moving a sound from stereo-center to one side or the other, either on a mixer or on a synthesizer, sequencer, etc. Usually this is not completely effective as panning alters only the relative amplitude of the sound left to right, and not the crucial aspect of delay. See Haas effect.
(3) One of the defined MIDI Controller Change messages assigned to the parameter in a synthesizer which determines the stereo image of the sound, effectively making that controller a panpot