A limerick is a funny, short, and random poem. A limerick has a rhyme scheme of aabba, meaning that the first two lines rhyme with the last line and the 3rd and 4th line rhyme. Limericks originated in England in the 18th century, but they became popular when  Edward Lear started to use the form in the 19th century.

There was an Old Person of Chili,
Whose conduct was painful and silly,
He sat on the stairs,
Eating apples and pears,
That imprudent Old Person of Chili.

Edward Lear