Terza rima is a verse form composed of iambic tercets (three-line groupings). The rhyme scheme for this form of poetry is "aba bcb cdc, etc." The second line of each tercet sets the rhyme for the following tercet, and thus supplying the verse with a common thread, a way to link the stanzas. The only time the form changes is at the conclusion of the poem, where the terza rima ends with either a single line or couplet repeating the rhyme of the middle line of the final tercet (like d or dd). There is no limit to the number of lines in terza rime.
"Ode to the West Wind."
by Percy Bysshe Shelley's
O wild West Wind, thou breath of Autumn's being,
Thou from whose unseen presence the leaves dead
Are driven, like ghosts from an enchanter fleeing,
Yellow, and black, and pale, and hectic red,
Pestilence-stricken multitudes: O thou,
Who chariotest to their dark wintery bed
The winged seeds, where they lie cold and low,
Each like a corpse within its grave, until
Thine azure sister of the Spring shall blow
Her clarion o'er the dreaming earth, and fill
(Driving sweet buds like flocks to feed in air)
With living hues and odours plain and hill:
Wild Spirit, which art moving everywhere;
Destroyer and preserver; hear, oh, hear!