A limerick is a short, humorous, often ribald or nonsense poem, especially one in five-line anapestic meter with a strict rhyme scheme (AABBA), which is sometimes obscene with humorous intent. The first two lines rhyme with the last line and the third and fourth line rhyme, and they are usually shorter. The form can be found in England as of the early years of the 18th century. It was also popularized by Edward Lear in the 19th century, although he did not use the term limerick.
A limerick by Edward Lear from A Book of Nonsense
There was an Old Man in a tree,
Who was horribly bored by a Bee;
When they said, 'Does it buzz?'
He replied, 'Yes, it does!'
'It's a regular brute of a Bee!'