Snooker is a cue sport that originated among British Army officers stationed in India in the second half of the 19th century. It is played on a rectangular table covered with a green cloth (or "baize"), with pockets at each of the four corners and in the middle of each long side. Using a cue stick and 21 coloured balls, players must strike the white ball (or "cue ball") to pot or pocket the remaining balls in the correct sequence, accumulating points for each pot. An individual game (or frame), is won by the player scoring the most points. A match is won when a player wins a predetermined number of frames.

In total there are 22 balls (15 red, 6 colour balls and a white cue ball), 52.5 mm or 2​1⁄16 inches in diameter. The points value of the balls is as follows:

Red 1 point

Yellow 2 points

Green 3 points

Brown 4 points

Blue 5 points

Pink 6 points

Black 7 points

More Info: en.wikipedia.org