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
Karpov, Kasparov, Korchnoi have absolutely destroyed chess by their immoral, unethical, prearranged games. These guys are really the lowest dogs around, and if people knew the truth about them, they would be held in more contempt than Ben Johnson, the runner, and they’re going to know the truth when I do this book!
Robert Fischer September, 1 1992
Danailov, in his campaign, used the motto – “I know.” One or two months later he said “I am learning.” Three years after, we know that he cannot learn. He gave so many promises, he has done absolutely nothing.
Georgios Makropoulos 2013
When you see a good move, look for a better one
Emanuel Lasker
There is no room for gallantry in chess.
Irving Chernev
Chess is respected in culture and education, but our organization is far behind. FIDE must lead, not drag chess down.
Garry Kasparov 2014