A polyphonic (from the Greek for 'many sounded') sound is one in which two or more melodic lines combined into a multivoiced texture, as distinct from monophonic ("one-sounding") and homophonic ("like-sounding"). The multiple musical lines may sound simultaneously, either in strict imitation of each other, or move in more independent fashion weaving in and out of each other. In the case of a musical instrument, polyphonic means the ability to play more than one note simultaneously. For example, a six-string guitar has a maximum of 6-note polyphony.
Counterpoint is almost synonymous with polyphony, but it usually refers to specific practices that were codified during the Baroque period – for example, the fugue.