This is a musical term in the medieval period. It usually refers to a dance, a tune played for dancing, or a song sung for or while dancing, often circle-dancing. It is also used for hymns intended to be sung, sung psalms and Christmas songs. Chaucer strongly associates carols with dancing and singing, especially by women and often as part of the courtly game of love.
Richard Leighton Greene, in his study of the Early English Carol, defines the two key features of this musical form: ‘All are in stanzas, the form of which is not changed in the course of the poem’ and ‘all have prefixed a group of lines which forms a burden or chorus, to be sung…before the first stanza and repeated after that and all succeeding stanzas’ (p. xxxi).