The difference between prose and poetry. For example:
"There was a young lady from the Khyber Pass,
Who went into the Ganges up to her knees."
That's prose. If she had gone a bit deeper it would have been poetry.
SUCCESS, n. The one unpardonable sin against one's fellows. In
literature, and particularly in poetry, the elements of success are
exceedingly simple, and are admirably set forth in the following lines
by the reverend Father Gassalasca Jape, entitled, for some mysterious
reason, "John A....