A quatern is a 16-line poem which originated in France. It is composed of four quatrains (4-line stanzas), with each line having eight syllables.
The poem has a refrain — a repeating line. The refrain is the first line of the first stanza, the second line of the second stanza, the third line of the third stanza, and the fourth line of the fourth stanza. Since the refrain is such an important part of the poem, when writing a quatern, it is a good idea to write the refrain first.