Terza rima is a poetic stanza of three lines used primarily by Italian poets. The rhyme structure is a b a, b c b, c d c, etc.
The most famous use of terza rima is in Dante's Divine Comedy. It is also the first known use, and was probably specifically invented by Dante to fit with the trinity theme of that epic. Petrarch and Boccaccio also made use of terza rima.
In his poem Complaint to His Lady, Geoffrey Chaucer uses a style similar to terza rima, though it does not strictly adhere to its rules. Thomas Wyatt was responsible for a burst of popularity that terza rima enjoyed in 16th century England.
Inferno - Dante
Nel mezzo del cammin di nostra vita
mi ritrovai per una selva oscura
esta selva selvaggia e aspra e forte
che nel pensier rinova la paura!
ma per trattar del ben ch'i' vi trovai,
Mine own John Poynz - Wyatt
Mine own John Poynz, since ye delight to know
The cause why that homeward I me draw,
And flee the press of courts, whereso they go,
Rather than to live thrall under the awe
To will and lust learning to set a law:
It is not for because I scorn or mock
The power of them, to whom fortune hath lent
Charge over us, of right, to strike the stroke