Fourteen lines of iambic pentameter that rhyme ABAB CDCD EFEF GG are called a Shakespearean sonnet. Note that this form ends with a couplet, but it’s not called a heroic couplet because it’s the only set of two in the poem. Petrarchan and Spenserian sonnets also use rhymed iambic pentameter in slightly different rhyme schemes. Lines of iambic pentameter in successive quatrains -- four-line stanzas -- that each rhyme ABAB, as in Thomas Gray’s “Elegy Written in a Country Churchyard,” are often called elegiac stanzas. Rhymed iambic pentameter can also occur in lyrical or narrative poetry, especially from the Romantic period; John Keats is particularly noted for this form, and his “Endymion” is an example of a pastoral narrative poem in heroic couplets.