From www.Poetry.org:
"The pantoum originated in Malaysia in the fifteenth-century as a short folk poem, typically made up of two rhyming couplets that were recited or sung. However, as the pantoum spread, and Western writers altered and adapted the form, the importance of rhyming and brevity diminished. The modern pantoum is a poem of any length, composed of four-line stanzas in which the second and fourth lines of each stanza serve as the first and third lines of the next stanza. The last line of a pantoum is often the same as the first."