A refrain (from Vulgar Latin refringere, "to repeat", and later from Old French refraindre) is the Line (poetry) or lines that are repeated in music or in Poetry; the "chorus" of a song. Poetry fixed forms that feature refrains include the villanelle, the virelay, and the sestina.

The use of refrains is particularly associated with where the Verse-chorus form song structure typically places a refrain in almost every song. The refrain or chorus often sharply contrasts the Verse (popular music) melody, rhythmically, and harmony, and assumes a higher level of dynamics (music) 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. See also verse-chorus form.

In music, a refrain has two parts: the lyrics of the song, and the melody. Sometimes refrains vary their words slightly when repeated; recognisability is given to the refrain by the fact that it is always sung to the same tune, and the rhymes, if present, are preserved despite the variations of the words. Such a refrain is featured in "The Star-Spangled Banner," which contains a refrain which is introduced by a different phrase in each verse, but which always ends:

:O'er the land of the free, and the home of the brave.

A similar refrain is found in the "Battle Hymn of the Republic," which affirms in successive verses that "Our God," or "His Truth." is "marching on."

Refrains usually, but not always, come at the end of the verse. Some songs, especially ballads, incorporate refrains into each verse. For example, one version of the traditional ballad The Twa Sisters includes a refrain mid-verse:

:There lived a lady by the North Sea shore,
::Lay the bent to the bonny broom
:Two daughters were the babes she bore.
::Fa la la la la la la la la.

:As one grew bright as is the sun,
::Lay the bent to the bonny broom
:So coal black grew the other one.
::Fa la la la la la la la.

:. . .

(Note : the refrain of 'Lay the Bent to the Bonny Broom' is not traditionally associated with the ballad of The Cruel Sister (Child #10). This was the work of 'pop-folk' group Pentangle on their 1970 LP 'Cruel Sister' which has subsequently been picked up by many folk singers as being traditional. Both the melody and the refrain come from the ballad known as Riddles Wisely Expounded (Child #1).)

Here, the refrain is syntax independent of the narrative poem in the song, and has no obvious relationship to its subject, and indeed little inherent meaning at all. The device can also convey material which relates to the subject of the poem. Such a refrain is found in Dante Gabriel Rossetti's Troy Town:

:Heavenborn Helen, Sparta's queen,
::O Troy Town!
:Had two breasts of heavenly sheen,
:The sun and moon of the heart's desire:
:All Love's lordship lay between,
:A sheen on the breasts I Love.
::O Troy's down,
::Tall Troy's on fire!

:. . .

Phrases of apparent nonsense in refrains (Lay the bent to the bonny broom?), and solfege syllables such as fa la la, familiar from the Christmas carol Deck the Halls with Boughs of Holly, have given rise to much speculation. Some believe that the traditional refrain Hob a derry down O encountered in some England folksongs is in fact an ancient Celtic languages phrase meaning "dance around the oak tree." These suggestions remain controversial.