Real Dictionary

fall off
phrasal verb: If something falls off, it separates from the thing to which it was attached and moves towards the ground.
phrasal verb: If the degree, amount, or size of something falls off, it decreases.

fall off in American English
to become smaller, less, lighter, etc.
to separate from; withdraw

fall off in British English
to drop unintentionally to the ground from (a high object, bicycle, etc), esp after losing one's balance
noun: a decline or drop

fall-off in British English
noun