Battery
Two or more long-range pieces aligned on the same line, attacking along it as a unit.
A battery is a stacked formation of pieces on the same file, rank, or diagonal, working together to attack along that line. The most common batteries are queen-and-rook on an open file, queen-and-bishop on a diagonal aimed at the enemy king, and two rooks doubled on the seventh rank.
The battery’s strength is that the front piece can capture or threaten, and the back piece supports it. An opponent who captures the front piece is immediately recaptured by the back one. This makes a battery much harder to neutralise than a single attacker on the same line.
The queen-bishop battery on the b1-h7 diagonal (or its mirror b8-h2 for Black) is a recurring middlegame theme. The bishop on d3 or c2 in front of the queen on b1 or c2 creates immediate threats against h7, and many attacks on a castled king involve building this battery and then sacrificing on h7.
A battery is created. It does not happen by accident. The move that places the second piece on the line is the battery move, and it often comes a tempo before the attack begins. The defender’s task is to neutralise the battery before it fires — by blocking the line with a pawn, by exchanging the front piece, or by trading the back piece for one of the same line.