What does a beat mean in limerick?

A beat in a limerick is a unit of rhythm. Each limerick line consists of three beats, with the exception of the last line, which has four beats. The beats are created by stressed syllables in the line. For example, the first line of the following limerick has three beats:

> There once was a man from Peru,

(stressed syllables: There | once | man)

The second line also has three beats:

> Who dreamt he was eating his shoe,

(stressed syllables: dreamt | eat | shoe)

The third line has three beats:

> He awoke in a fright,

(stressed syllables: a | woke | fright)

The fourth line has three beats:

> In the middle of the night,

(stressed syllables: mid | dle | night)

And the fifth line has four beats:

> And he found it was perfectly true.

(stressed syllables: found | was | per | fect)