For the communications operator see Chorus Communications

For the computer operating system see ChorusOS

In classical music a chorus is any substantial group of performers in a play, revue, musical or opera who act more or less as one. It can also mean a work, or section of a work, performed by a chorus. Today, it is most usually used as a synonym for choir to mean a group of singers who all sing together or a piece sung by such a group, but it can also mean a group of dancers, and in Greek drama it meant a group of actors (see also: Greek chorus).

In popular music, chorus is used to mean the refrain of a song, which often sharply contrasts the verse melodically, rhythmically, and harmonically, and assumes a higher level of dynamics and activity, often with added instrumentation. Chorus form, or strophic form, is a sectional and/or additive way of structuring a piece of music based on the repetition of one formal section or block played repeatedly.

In music technology, chorus is an effect caused by taking an audio signal and mixing it with several delayed copies of itself and/or several pitch-shifted copies of itself. The resulting sound simulates the sound of several instruments or voices where there is really only one. Stereo chorus produces the same effect, but the chorus effect varies between the left and right channels.