Limerick

Special verse form characterized by its closed structure. The final word of the first line was repeated at the end of the last line. The typical rhyme scheme is aabba. Often with humorous intent in which the characters always behave according to the rules of "nonsense". The characters in Limericks always show some peculiar idiosyncrasy (concerning their behaviour or appearance) which distinguishes them from the rest of society."In its most typical form it announces the existence of the eccentric, notes his dwelling place, and describes his distinctive features; then it explains the consequences of his peculiarity and concludes with an apostrophe."(http://www.poetryfoundation.org/bio/edward-lear.