From http://www.rane.com/par-p.html:
See also Audio Polarity Test.
See also phase reverse.
A signal's electromechanical potential with respect to a reference potential. For example, if a loudspeaker cone moves forward when a positive voltage is applied between its red and black terminals, then it is said to have a positive polarity. A microphone has positive polarity if a positive pressure on its diaphragm results in a positive output voltage. [Usage Note: polarity vs. phase shift: polarity refers to a signal's reference NOT to its phase shift. Being 180° out-of-phase and having inverse polarity are DIFFERENT things. We wrongly say something is out-of-phase when we mean it is inverted. One takes time; the other does not.]
See also Audio Polarity Test.
See also phase reverse.