Position

In everyday use, a position is the way the pieces are arranged on the board at a particular moment. For exact analysis or reconstruction, visible placement is not always enough: the side to move and any remaining special rights also matter.

What defines the current state

• The square occupied by every piece.
• The side whose turn it is to move.
• Castling rights, meaning whether each king and the relevant rook still retain the rule-based possibility of making that special move.
• Any immediate en passant possibility, a special pawn capture that can exist only just after a particular opposing two-square pawn advance.
• The number of individual turns since the last pawn move or capture. This helps apply the 50- and 75-move rules, which can end the game as a draw, a result with no winner.

Two diagrams with pieces on the same squares can describe different positions if the turn, castling rights, or en passant possibility differs. Under the rules, an illegal position is one that could not have been reached from the starting position by any sequence of legal moves, meaning moves permitted by the rules.

Applying repetition rules also requires the game history: an isolated position does not say how many times an equivalent state appeared earlier. The fullmove number, which advances after each Black move and is commonly included in technical records, helps locate the moment within a game, but it does not by itself change the legal moves.

The phrase “White has the better position” adds an evaluation: it is a judgment about each side's prospects, not another part of the state itself. Players and a chess engine, a program that calculates moves and estimates their consequences, may evaluate the same position differently.