in medieval French literature, a short romance, usually written in octosyllabic verse, that dealt with subjects thought to be of Celtic origin. The earliest lay narratives were written in the 12th century by Marie De France; her works were largely based on earlier Breton versions thought to have been derived from Celtic legend. The Breton lay, a 14th-century English poetic form based on these lays, is exemplified by “The Franklin's Tale” in Geoffrey Chaucer (Chaucer, Geoffrey)'s The Canterbury Tales.

The term lay may refer to a medieval lyric poem. The earliest extant examples are those composed by Gautier de Dargies in the 13th century. These lays had nonuniform stanzas of about 6 to 16 or more lines of 4 to 8 syllables. One or two rhymes were maintained throughout each stanza.

A lay may be a song, a melody, a simple narrative poem, or a ballad, such as those written in the early 19th century by Sir Walter Scott (Scott, Sir Walter, 1st Baronet) and Thomas Macaulay (Macaulay, Thomas Babington Macaulay, Baron).