Chess is an abstract strategy board game for two players. It is played on a square board of eight rows (called ranks) and eight columns (called files), giving 64 squares of alternating colour, light and dark, with each player having a light square at the near right corner when facing the board. Each player begins the game with 16 pieces which can move in defined directions (and in some instances, limited range) and can remove other pieces from the board: each player's pieces comprise eight pawns, two knights, two bishops, two rooks, one queen and one king. One player controls the white pieces; the other player controls the black pieces (the player that controls white is always the first player to move).
In chess, when a player's king is directly threatened by one or more of the opponent's pieces, the player is said to be in 'check'. When in check, only moves that can avoid check, block check or take the offending piece are permitted. The object of the game is to checkmate the opponent; this occurs when the opponent's king is in check, and no move can be made that would escape from check.
Chess is not a game of chance; it is based solely on tactics and strategy. Nevertheless, the game is so complex that not even the best players can consider all contingencies: although only 64 squares and 32 pieces are on the board, the number of possible games that can be played far exceeds the number of atoms in the universe.
Chess is one of the world's most popular games; it has been described not only as a game but also as an art and a science. Chess is sometimes seen as an abstract wargame; as a "mental martial art", and teaching chess has been advocated as a way of enhancing mental prowess. Chess is played both recreationally and competitively in clubs, tournaments, online, and by mail (correspondence chess).