A situation when a piece or a pawn cannot or is forbidden to move because it could expose the king for an attack or would expose a more valuable piece behind it to capture.
In the following example Qa3 and Re7 are pinned.
ECHESSPEDIA
Quotes of the Day
When I am in the USSR, I have the feeling that every tram conductor plays chess better than I do.
Hans Ree
Tal develops all his pieces in the centre and then sacrifices them somewhere.
David Bronstein
Chess should not become an obsession. Otherwise there’s a danger that you will slide off into a parallel world, that you lose your sense of reality, get lost in the infinite cosmos of the game. You become crazy.
Magnus Carlsen 2010
One of the most important things in chess is pattern recognition: the ability to recognise typical themes and images on the board, characteristics of a position and their consequences.
Magnus Carlsen 2010
As a rule, pawn endings have a forced character, and they can be worked out conclusively.
Mark Dvoretsky