Rhythm

Definition: pattern of stressed and unstressed syllables in a line of a poem. 

Example:

There was an old man from Peru,
Who dreamed he was eating his shoe
He awoke in the night
With a terrible fright
And found out it was quite true

Significant: Rhythm is is significant in poetry because poetry is so emotionally charged and intense. It created emotions and feelings for the poems, more fun to read, and interesting.