In poetry, a tetrameter is a line of four metrical feet:

And the sheen of their spears was like stars on the sea (Anapaest tetrameter) (Byron, "The Destruction of Sennacherib")

"You who are bent and bald and blind" (Iambic tetrameter, except for the first foot which is a trochee) (Yeats, "The Wanderings of Oisin")

"Peter, Peter, pumpkin-eater" (trochaic tetrameter)

External Links

Tetrameter.com A website devoted to verse in tetrameter