In poetry, one or two identical lines recurring at the end of each stanza of a strophic poem.  In a musical composition, each repetition of the refrain is, of course, set to the same melody, so that the term refers to both textual and musical repetition.  The refrain is often called "chorus" since it is often sung by the full chorus while the stanzas (verses) are solo.

In the antiphonal and responsorial singing of the early Christian Church, an exclamation such as Amen, Alleluia, or a short phrase was repeated by the congregation or choir after each psalm verse or pair of verses.  The refrain poem, cultivated in the 12th and 13th centuries by the trouveres, was the basis for various refrain forms such as the formes fixes.