Pin
A pin ties a piece to its square: a bishop, rook or queen attacks it, and stepping aside would expose a more valuable piece standing behind it on the same line.
In practice: pins are won by adding attackers, so count how many pieces attack the pinned piece and how many defend it before you decide how to meet one.
Picture three pieces on one line: your attacker, an enemy piece, and something more valuable of theirs standing behind. The piece in the middle is pinned. Only bishops, rooks and queens can create this picture, because they are the pieces that attack along lines.
What makes a pin useful is pressure. A pinned piece cannot easily run, so you pile on: attack it with a pawn, add a second attacker, or threaten the piece behind it directly. Often the pinned piece falls without a single capture along the pinning line.
There are two flavours. If the piece behind is the king, the rules bar the pinned piece from leaving the line, and this is called an absolute pin. If the one behind is merely valuable, moving is legal but expensive, which is a relative pin. Each has its own entry in this glossary.
When you are the one pinned, you have four ways out: move the valuable piece, block the line, capture the pinner, or support the pinned piece so that a trade works for you. Breaking a pin early is cheaper than defending a pinned piece for ten moves.
In the diagram White plays Bg5. The bishop looks at the knight on f6, and behind the knight on the same diagonal stands a rook on e7. If the knight leaves, Bxe7 wins the rook.
A neighboring idea is Overloading. Overloading is a tactic against a single defender that has two jobs at once, so that when you win one of the things it guards, it can no longer protect the other.
Compare it with X-ray attack. An x-ray is hidden pressure: a bishop, rook or queen bears on a piece or square beyond an enemy piece in its way, and the pressure turns real once the blocker moves or is exchanged.
It sits close to Tactical motif. A tactical motif is a recurring pattern, such as a fork, pin or skewer, that appears often enough in games to be recognized and reused as the basis of a combination.
Knowing "Pin" helps most once you can spot it in a real game. A first lesson with George Li starts from your own games and finds the tactics you keep missing.
Related terms
An absolute pin is a pin in which the piece behind the pinned piece is the king, so the pinned piece cannot legally move off the line at all.
A relative pin is a pin in which the piece behind the pinned piece is more valuable but is not the king, so the pinned piece may legally move but would lose that piece.
A skewer attacks a valuable piece that stands in front of a less valuable one on the same line. The front piece must run, and the piece behind it is then taken.
In a discovered attack one of your pieces steps off a line, and that move unmasks a bishop, rook or queen standing behind it, so a single turn produces two threats.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
How much does chess coaching cost?
Published rates for private, group and subscription chess coaching, with the source and the date of each.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.