Question

Anyone knows that? What is a Limerick?

Answer 1

A silly, short, and rhyming poem.

Answer 2

A limerick is a particular kind of short poem.  What makes it a limerick
is its unique physical structure:

2 long lines
2 short lines
1 long line.

When you hear one, you know it right away.

Example:

The limerick packs laughs anatomical
Into space that is quite economical.
. . . . . But the good ones I've seen
. . . . . So seldom are clean
And the clean ones so seldom are comical.

A number of leading playwrights and authorities on language
have expressed the opinion that a true limerick is always dirty.