The word pool generally refers to pocket billiard games such as 8-ball, 9-ball, or Straight pool. The word pool comes from pool rooms, where people gambled off track on horse races. They were called poolrooms as money was "pooled" to determine the odds. These rooms commonly provided billiard tables, and by association pool became synonymous with billiards. The terms pool and pocket billiards are synonymous.
All billiards games are generally regarded to have evolved into indoor games from outdoor stick and ball games.
The word billiard may have evolved from the French word 'billart' which means mace, the forerunner to the modern cue.