Scrabble have been sold worldwide and roughly one-third of American and half of British homes have a Scrabble set. There are around 4,000 Scrabble clubs around the world. The game is played by two to four players on a square board with a 15×15 grid of cells (individually known as "squares"), each of which accommodates a single letter tile. In official club and tournament games, play is between two players or, occasionally, between two teams each of which collaborates on a single rack. The board is marked with "premium" squares, which multiply the number of points awarded: eight dark red "triple-word"
English-language Scrabble also carry significant prize money. The official dictionary is the Official Tournament and Club Word List. When a player challenges a word he considers to be invalid, if the word is invalid it is removed from the board with a score of zero. However if the word is valid, the player who challenged the word loses his turn. Scrabble clubs are also run that meet on a regular basis, usually weekly or biweekly at the same venue. Players usually play a smaller number of games than they would play at a tournament. Match play Scrabble is also practised at tournament