A limerick is a five-line poem with a strict meter, popularized by Edward Lear. The rhyme scheme is usually aabba. The first, second, and fifth lines are three metrical feet (9 syllables); the third and fourth are two metrical feet (One metrical foot is equal to 3 syllables; the line pattern goes 9-9-6-6-9). The foot used is usually the amphibrach, a stressed syllable between two unstressed ones. However, many substitutions are common, notably the anapestic foot, two short syllables and then a long (the reverse of dactyl rhythm).
The first line traditionally introduces a person and a location, and usually ends with the name of the location, though sometimes with that of the person. A true limerick is supposed to have a kind of twist to it. This may lie in the final line, or it may lie in the way the rhymes are often intentionally tortured, or in both. Though not a strict requirement, many limericks additionally show some form of internal rhyme, often alliteration, sometimes assonance or another form of rhyme. In early limericks, the last line often essentially repeated the first, though that is no longer customary.