Chess is a board game for two players. It is sometimes called international chess or Western chess to distinguish it from related games such as xiangqi and shogi.
Chess strategy is the aspect of chess play concerned with evaluation of chess positions and setting goals and long-term plans for future play. While evaluating a position strategically, a player must take into account such factors as the relative value of the pieces on the board, pawn structure, king safety, position of pieces, and control of key squares and groups of squares. Chess strategy is distinguished from chess tactics, which is the aspect of play concerned with the move-by-move setting up of threats and defenses. Some authors distinguish static strategic imbalances, which tend to persist for many moves, from dynamic imbalances, which are temporary. This distinction affects the immediacy with which a sought-after plan should take effect. Until players reach the skill level of "master", chess tactics tend to ultimately decide the outcomes of games more often than strategy. Many chess coaches thus emphasize the study of tactics as the most efficient way to improve one's results in serious chess play.
The king is the most important piece in the game of chess. It may move to any adjoining square; it may also perform, in tandem with the rook, a special move called castling. If a player's king is threatened with capture, it is said to be in check, and the player must remove the threat of capture immediately. If this cannot be done, the king is said to be in checkmate, resulting in a loss for that player. A player cannot make any move that places their own king in check. Despite this, the king can become a strong offensive piece in the endgame or, rarely, the middlegame.
The rules of chess govern the play of the game of chess. Chess is a two-player abstract strategy board game. Each player controls sixteen pieces of six types on a chessboard. Each type of piece moves in a distinct way. The object of the game is to checkmate the opponent's king; checkmate occurs when a king is threatened with capture and has no escape. A game can end in various ways besides checkmate: a player can resign, and there are several ways a game can end in a draw.
This glossary of chess explains commonly used terms in chess, in alphabetical order. Some of these terms have their own pages, like fork and pin. For a list of unorthodox chess pieces, see Fairy chess piece; for a list of terms specific to chess problems, see Glossary of chess problems; for a list of named opening lines, see List of chess openings; for a list of chess-related games, see List of chess variants; for a list of terms general to board games, see Glossary of board games.
Atomic chess is a chess variant. Standard rules of chess apply, but all captures result in an "explosion" through which the capturing piece, captured piece, and all surrounding pieces of both colors other than pawns are removed from play. Some variations additionally remove rules concerning check such that the king may be able to move into or remain in check.
In chess, a tactic is a sequence of moves that each makes one or more immediate threats – a check, a material threat, a checkmating sequence threat, or the threat of another tactic – that culminates in the opponent's being unable to respond to all of the threats without making some kind of concession. Most often, the immediate benefit takes the form of a material advantage or mating attack; however, some tactics are used for defensive purposes and can salvage material that would otherwise be lost, or to induce stalemate in an otherwise lost position.
Vernon Rylands Parton was an English chess enthusiast and prolific chess variant inventor, his most renowned variants being Alice chess and Racing Kings. Many of Parton's variants were inspired by the fictional characters and stories in the works of Lewis Carroll. Parton's formal education background, like Lewis Carroll's, was in mathematics. Parton's interests were wide and he was a great believer in Esperanto.
Crazyhouse is a chess variant in which captured enemy pieces can be reintroduced, or dropped, into the game as one's own. It was derived as a two-player, single-board variant of bughouse chess.
In chess and similar games, check is a condition that occurs when a player's king is under threat of capture on the opponent's next turn. A king so threatened is said to be in check. A player must get out of check if possible by moving the king to an unattacked square, interposing a piece between the threatening piece and the king, or capturing the threatening piece. If the player cannot remove the check by any of these options, the game ends in checkmate and the player loses. Players cannot make any move that puts their own king in check.
Cylinder chess is a chess variant. The game is played as if the board were a cylinder, with the left side of the board joined to the right side. Cylinder chess is one of six chess variants described by the Arabic historian Ali al-Masudi in 947.
In chess, promotion is the replacement of a pawn with a new piece when the pawn is moved to its last rank. The player replaces the pawn immediately with a queen, rook, bishop, or knight of the same color. The new piece does not have to be a previously captured piece. Promotion is mandatory when moving to the last rank; the pawn cannot remain as a pawn.
The touch-move rule in chess specifies that a player, having the move, who deliberately touches a piece on the board must move or capture that piece if it is legal to do so. If it is the player's piece that was touched, it must be moved if the piece has a legal move. If the opponent's piece was touched, it must be captured if it can be captured with a legal move. If the touched piece cannot be legally moved or captured, there is no penalty. This is a rule of chess that is enforced in all formal over-the-board competitions.
Shogi, like western chess, can be divided into the opening, middle game and endgame, each requiring a different strategy. The opening consists of arranging one's defenses and positioning for attack, the middle game consists of attempting to break through the opposing defenses while maintaining one's own, and the endgame starts when one side's defenses have been compromised.
The following outline is provided as an overview of and topical guide to chess:
Dragonfly is a chess variant invented by Christian Freeling in 1983. There are no queens, and a captured bishop, knight, or rook becomes the property of the capturer, who may play it as their own on a turn to any open square. The board is 7×7 squares, or alternatively a 61-cell hexagon with two additional pawns per side.
Dynamo chess is a chess variant invented by chess problemists Hans Klüver and Peter Kahl in 1968. The invention was inspired by the closely related variant push chess, invented by Fred Galvin in 1967. The pieces, board, and starting position of Dynamo chess are the same as in orthodox chess, but captures are eliminated and enemy pieces are instead "pushed" or "pulled" off the board. On any given move, a player can make a standard move as in orthodox chess, or execute a "push move" or a "pull move". A move that is either a push move or a pull move is called a "dynamo move".
Many basic tactics of shogi are similar to those of chess tactics, involving forks, pins, removing the defender and other techniques, all of which are considered very strong when used effectively.
Online chess is chess that is played over the Internet, allowing players to play against each other. This was first done asynchronously through PLATO and email in the 1970s. In 1992, the Internet Chess Server facilitated live online play via telnet, and inspired several other telnet-based systems around the world. Web-based platforms became popular in the 2010s and grew considerably amid the COVID-19 pandemic, alongside a trend of livestreaming chess.
