A limerick is a structured poem in which the following
(1) Rhyme the ends of lines 1,2, and 5.
(2) Rhyme the ends of lines 3 and 4.
(3) The specified lines must not rhyme with
each other, meaning, 1, 2, and 5 cannot rhyme
with 3 and 4.
(4) Line one must introduce a character, and if
you like, a place.
(5) Line two should tell something about the character.
(6) Lines 3, and 4 should allow some sort of
action to occur.
(7) Line 5 should complete the poem, usually
with a funny ending.
See example below...