The limerick is a form of poetry usually containing some form of comedy or comical "storytelling."  They follow a strict AABBA rhyme scheme, in which the "B" lines are usually shorter than the "A" lines.  This form of poetry dates back to the early 1800's in England, but was not very popular until Edward Lear published and brought limericks to the public eye.  Despite his constant usage of the limerick poem form, Lear never called his poetry "limericks."  Often seen as "unprofessional" and "mediocre," the limerick has never been the most popular form of poetry, especially due to its lack of ability to have a lot of "real meaning."  Be that as it may, the limerick is a very popular and fun form of poetry that will be read ad written by many to come.

Example Poem

Old Man With a Beard

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!'

-Edward Lear