A limerick is a short, humorous, and sometimes musical poem. It became popular in English in the 19th century by Edward Lear. The first, second, and fifth longer lines rhyme. The third and fourth shorter lines rhyme. The longer lines should have seven to ten syllables, and the shorter lines should have five to seven syllables.
There Was an Old Man With a Beard by Edward Lear
There was an Old Man with a beard,
Who said, “It is just as I feared!—
Two Owls and a Hen, four Larks and a Wren,
Have all built their nests in my beard!