A small and rather deep collection of (usually) fresh water, as one supplied by a spring, or occurring in the course of a stream; a reservoir for water.

“the pools of Solomon”

A small body of standing or stagnant water; a puddle.

A supply of resources.

“There is a limited pool of candidates from which to choose the new manager.”

(of a liquid) To form a pool.

A pool of water used for swimming, usually one which has been artificially constructed.