Scrabble is a word game in which two to four players score points by forming words from individual lettered tiles on a game board marked with a 15-by-15 grid. The words are formed across and down in crossword fashion and must appear in a standard dictionary. Official reference works (e.g. The Official Scrabble Players Dictionary) provide a list of permissible words. The Collins Scrabble checker can also be used to check if a word is allowed. The name Scrabble is a trademark of Hasbro, Inc. in the United States and Canada. Elsewhere, Scrabble is trademarked by Mattel. The game is sold in 121 countries; there are 29 different language versions. One hundred and fifty million sets have been sold worldwide, and sets are found in roughly one-third of American homes.