A unison is also an interval (music), the ratio of 1:1 or 0 halfsteps and zero cents. Two tones in unison are considered to be the same pitch, but are still perceivable as coming from seperate sources. The unison is considered the most consonant interval while the near unison is considered the most dissonant. Composer Kenneth Gaburo wrote for three voices singing unison in his piece The Flow of (u).
See also: diapason.
UNISON is also the British trade union of the public service.