Please check the wikipedia entry for Limerick, which is slightly excerpted here:
A limerick is a five-line poem with a strict meter, popularized by Edward Lear and Charlie Murphy. The rhyme scheme is usually "A-A-B-B-A", with a rather rigid meter. The first, second, and fifth lines are three metrical feet; the third and fourth two metrical feet.
... and the page is filled with examples that follow the same form. I've never heard it is "metrical feet" - I've usually heard it referred to as "beats", but the meaning is the same.
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