Pantoum
Rules quoted from the poets.org glossary; examples only from public-domain poems.
The rules, quoted
The 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.
Our explanation written by Tale of the Muse
A pantoum can run to any length in four-line stanzas, and repetition drives it: the second and fourth lines of each stanza become the first and third lines of the next. The glossary adds that the last line is often the same as the first, which closes the loop.
Our plain-language restatement of the glossary rules above. It adds no facts of its own.
Example
No public-domain example is shown for this form.