Walk into a bar or private rec room and you're likely to encounter a pool table, with patrons and guests leaning over a green felt surface and striking a white cue ball with a cue stick in an effort to sink the rest of the balls into six pockets. If you're invited to join, most people will ask about a game of pool, not a game of billiards. Yet both terms seemingly refer to the same activity. What's the difference?
According to the Billiard Congress of America, billiards was developed out of a lawn game similar to croquet in the 15th century. When play moved indoors, green tables were used to simulate grass. Originally, the balls in billiards were driven by a mace with a large tip instead of a stick and through something similar to a croquet wick. The game evolved and expanded over time to include pocketed tables and shot-calling for points, enjoying wide popularity in America in the 1920s. The term billiards comes from the French words billart ("wooden stick") and bille ("ball").
As the popularity of billiards grew, billiards tables became common sights in gambling parlors where horse racing wagers or other bets were being placed. Because a collection of wagers is known as a pool, pocket billiards began to be associated with the term. Some professional pool players still use the term billiards to describe what's more commonly known as pool. Typically, billiards can refer to any kind of tabletop game played with a cue stick and cue ball, while pool largely means a game with pockets.
In the UK, however, billiards can refer to English Billiards, a variation in which only three balls are used, with the player striking his cue ball and a red striker ball to move his opponent's cue ball. There are no pockets used in the game.
You may wonder where this leaves snooker, an even more obscure game. Since it's played with a cue and a cue ball, it's technically billiards, but snooker has a specific rule set involving 22 balls that need to be sunk with consideration given to each color's point value. At 10 to 12 feet in length, a snooker table is also larger than a conventional pool surface (from 7 to 9 feet) and its pockets are an inch smaller in diameter.
The bottom line? If you're in a social setting and get challenged to a game of billiards, it's probably going to be pool. If you're in the UK, it could mean the pocket-less version. And if you get challenged to a game of snooker, be prepared for a very lengthy explanation of the rules.