A limerick is a short, often humorous and ribald poem developed to a very specific structure.
The rhyme scheme is usually aabba, with a very rigid meter. The first, second, and fifth lines are three metrical feet; the third and fourth two metrical feet. The rhythm can be called an anapestic foot, two short syllables and then a long, the reverse of dactyl rhythm. The first line often ends with a person's name or a location (geographical limericks), and rhymes are often intentionally tortured. Iambs are often substituted for an initial anapestic foot.