Of the six types of chess piece, the line pieces -- Queen, Rook, and Bishop -- are the three pieces that move in straight lines. They move in straight lines in any legal direction.
Open lines are ranks, files, and diagonals that aren't obstructed by Pawns. Queens and Rooks favor open ranks and files, while Queens and Bishops love open diagonals.
Kings and Pawns aren't line pieces because they only move one square at a time (two squares for a Pawn's first move, but that doesn't change anything). Knights aren't line pieces because they move in an L-shape and can hop over obstructions.
The line pieces are blocked whenever their line is obstructed. If a line is obstructed by an enemy piece, at least the line piece is attacking something. If it's a friendly piece, better that it be something other than a Pawn, which can't get out of the way quickly.
The more squares that are available on an open line, the better. The longest open lines have no obstructions of any kind. In a single move.
- a Queen on an open rank can shift from Kingside to Queen side;
- a Rook on an open file can shift from its own side to the enemy side; or
- a Bishop on an open diagonal can shift from one corner to another.
The more open lines available to a piece, the better. A Rook which can move to all squares on its rank and to all squares on its file is a powerful piece.
See Positional Play (under 'Suggested Reading') for more about
- Open lines
- Piece activity
