An open position is one where central pawns have been exchanged, leaving open files and diagonals where piece activity dominates.
Openness is a property of the center. When the d and e pawns get traded, lines through the middle of the board clear, and the game becomes about pieces: who develops faster, who controls the open files, whose bishops breathe.
In open positions, time is worth more and bishops usually outrank knights, since their long diagonals are unobstructed. Every tempo counts because contact happens immediately: a lag of two developing moves can lose by force, which is rarely true in a blocked structure.
Play open positions with urgency: develop toward the center, castle early, contest the open files with rooks, and avoid pawn-grabbing expeditions with the queen. Tactical alertness matters on every move, because open lines mean everything is always one move from being attacked.
The central pawns. Traded central pawns mean open files and diagonals and an open position; interlocked central chains mean a closed one. Many positions sit in between, semi-open, with one file open.
A bishop's power depends on unobstructed diagonals. With the center cleared, a bishop sweeps the whole board, while a knight still hops the same short distance. In blocked centers the judgment flips.
BetterChess is a practice tool — we make no guarantee you'll reach 1800 or any rating. Definitions are standard chess terminology; every diagram position is checked legal with the same engine the board runs.