Meaning of “pocket” - Learner’s Dictionary

pocket

noun [ C ] uk us /ˈpɒkɪt/
BAG

A2 a small bag that is sewn or fixed onto or into a piece of clothing, a bag, the back of a seat, etc:

a coat/shirt/trouser pocket
He was asked to empty his pockets.
Safety instructions are in the pocket on the seat in front of you.
SMALL AREA/AMOUNT

a small area or small amount of something that is different from what is around it:

There was real poverty in some pockets of the country.
small pockets of air trapped inside the glass
MONEY

the amount of money that you have for spending:

I shouldn't have to pay for travel out of my own pocket (= with my own money).
be out of pocket

to have less money than you should have because you have paid for something:

The travel company cancelled our trip and we were left hundreds of pounds out of pocket.

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