Meaning of “behind” - Learner’s Dictionary

behind

adverb uk us /bɪˈhaɪnd/
BACK

A2 at or to the back of someone or something:

Somebody grabbed me from behind.
SLOWER

slower or later than someone else, or than you should be:

She's behind with the rent (= is late to pay it).
PLACE

A2 in the place where someone or something was before:

You go on ahead. I'll stay behind and tidy up.
When we got to the restaurant, I realized that I had left my purse behind.

(Definition of “behind adverb” from the Cambridge Learner’s Dictionary © Cambridge University Press)