Short for stereophonic. Common usage of the term stereo would have it be defined as any sound reproduction (or reproduction system) with two speakers, typically a left channel and a right channel. Stereophonic, however, refers to any system that provides the listener with an illusion of directional realism, regardless of how many channels are used. The convention of using two channels to make stereo came about in the mid 1900′s mostly due to cost considerations and the relative ease of recording two channels in the groove of a phonograph record.