Narrative Poems
The longest poems tend to be narrative poems; that is, poems that tell a story. A narrative long enough to be its own book is generally called an epic. Homer's "Odyssey" and John Milton's "Paradise Lost" are two famous examples of epic poems. Ballads are poems that tell a simple, dramatic tale and employ a repeating stanza. They were originally written to be set to music. Idylls tell about heroes of past eras, while a lay is a narrative poem which was sung by medieval minstrels.
Special Occasion Poems
Certain kinds of poems are named after the occasion for which they are written. An elegy is a poem written in commemoration of someone who has died. Similarly, an epitaph may be a short, rhyming poem inscribed on a grave stone. On the other end of the spectrum, an epithalamion, or epithalamium, is a celebratory wedding poem written to give honor to the bride and groom.
Short Poems
A couplet is two rhyming lines; many longer poems employ couplets in them. In some cases, the couplet itself can be the poem. An epigram, for instance, is rhyming satire that is either two or four lines long. Other short poems include limericks, which are funny five-line poems still in use today; and haikus. Probably the most famous of Japanese poetry forms, a haiku has three unrhymed lines where the first line has five syllables, the second has seven and the third has five again.
Odes and Sonnets
Among English poetry, two forms that have earned particular notice are the ode and the sonnet. An ode is a rather long, serious, reflective poem with structured, rhyming stanzas. John Keats's "Ode on a Grecian Urn" is a well-known example. Sonnets are some of the most highly structured poetry forms; they have exactly 14 lines with 10 syllables in each line, and must conform to one of three different rhyme schemes. Shakespeare wrote 154 sonnets and the form he used has come to be known as the Shakespearean Sonnet.