What is a defining characteristic of a limerick?

A defining characteristic of a limerick is its specific meter and rhyme scheme. Limericks consist of five lines with a distinct rhythmic pattern, typically anapestic meter, where the first, second, and fifth lines contain three metrical feet, while the third and fourth lines contain two metrical feet. The rhyme scheme is also specific: it follows an AABBA pattern. This structured format gives limericks their catchy, playful quality and often humorous or whimsical themes.

The other choices represent different poetic forms or structures that do not apply to limericks. For instance, free verse poems lack a set meter or rhyme scheme, quatrains consist of four lines rather than the five found in limericks, and lengthy narrative poems generally tell a story over a longer span, rather than the shorter, often silly or nonsensical nature of a limerick.