Why is the game pool called pool?

Pocket billiards is very often called pool. The reason is simple...back in the day, circa turn of the century, rooms for betting on the horses were extremely prevalent.

The horse betting pools were such that these rooms were called pool rooms for short. Because pocket billiards became so popular with men of the day, pocket billiards tables were installed in most of these "horse betting pool" rooms.

Rapidly.."pool room" became known as a room with pocket billiard tables in it, and the pocket billiard game itself took on the misnomer.."pool".