Pool

The word pool refers to many different things:

A pool is a body of water. It is also called a pond. It can also mean a body of water that people have made. This is called a swimming pool.
Pool is also a game. It is a form of billiards. The object is to use a cue ball to knock other balls into pockets around the edge of the table.
People also use the word "pool" to mean something many people have contributed to. People can pool their money to buy something, or to make a bet. Sometimes it can mean cooperation, people working together to get something done.