Open file
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In chess, an open file is a file with no pawns. In the diagram, the e-file is an open file. An open file can provide a line of attack for a rook or queen. Having rooks and/or queens on open files and/or semi-open files is considered an advantage as it allows one to attack more easily. The objective of any open file is to reach the 7th/8th ranks (for White). Controlling the 7th rank is generally worth at least a pawn. Many games are decided based on this strategy.
See also half-open file.