A Limerick is a form of verse in five-line predominantly with a strict rhyme scheme of AA-BB-A, in which the first, second and fifth line rhyme, while the third and fourth lines are shorter and share a different rhyme. The following example is a Limerick of unknown origin:
The limerick packs laughs anatomical
Into space that is quite economical.
But the good ones I’ve SEEN,
So seldom are CLEAN,
And the clean ones so seldom are comical.
The form appeared in England in the early years of the18th century. It was popularized by Edward Lear in the 19th century. The exchange of Limericks is almost exclusive to comparatively well-educated males, women figuring in Limericks almost exclusively as “villains or victims”. The most prized limericks incorporate humour and a kind of twist, which may be revealed in the final line or lie in the way the rhymes are often intentionally tortured, or both. The origin of the name Limerick for this type of poem is debated. The name is generally taken to be a reference to the City or County of Limerick inIreland and may derive from an earlier form of nonsense verse parlour game (source: Wikipedia).