Terza Rima.

Italian form made famous by Dante in The Divine Comedy (though to the best of my knowledge, Sayer's translation is the only one that maintains the integrity of the form).

Interlocking tercets written in iambic pentameter rhyming aba bcb cdc and so forth. The final stanza is generally a couplet rhyming with the second line of the previous tercet. An example of a four stanza Terza Rima would be aba bcb cdc dd.