Terza Rima
A Verse Form Invented by Dante Allighieri
A fairly straightforward verse form. It doesn't prescribe a set metre, but in English the iambic pentameter is often used. It consists of a series of three-line stanzas, or tercets, which are linked in that the middle line of a stanza provides the rhyme for the first and third line for the subsequent one. The poem closes with a single line (or occasionally a couplet) which rhymes with the middle line of the preceeding stanza. The rhyme scheme used is therefore: aba bcb cdc [etc] ded[e].
This is an example from Robert Frost. It is a variation from the standard form since it finishes with a rhymed couplet.
Acquainted with the Night
                   I have been one acquainted with the night.                    I have looked down the saddest city lane.                    I have stood still and stopped the sound of feet                    But not to call me back or say good-by;                    Proclaimed the time was neither wrong nor right. A Note on Formal and Free Verse
                   I have walked out in rain - and back in rain.
                   I have outwalked the furthest city light
                   I have passed by the watchman on his beat
                   And dropped my eyes, unwilling to explain.
                   When far away an interrupted cry
                   Came over houses from another street,
                   and further still at an unearthly height
                   One luminary clock against the sky
                   I have been one acquainted with the night.