In poetry, a pentameter is a line of verse consisting of five metrical feet. Iambic pentameter is one of the most commonly used meters in English, used extensively by many poets, including William Shakespeare, John Milton, and William Wordsworth. It is a line that consists of five iambs. Occasionally, Shakespeare will invert each foot to produce a line in trochaic pentameter, which consists of five trochees; an example of which may be found in King Lear's dying speech--"Never, never, never, never, never!" (5.3).
The following is an illustration of iambic pentameter and a text example:
x 'x | x 'x | x 'x | x 'x | x 'x
"Shall I compare thee to a summer's day?" "O woe is me."