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
I think the players in this world championship are in different leagues. Karjakin is excellent—Carlsen is special.
Garry Kasparov 2016
I understood that through chess I could express myself and chess became my natural language.
Boris Spassky 1995
Chess is a game by its form, an art by its content and a science by the difficulty of gaining mastery in it. Chess can convey as much happiness as a good book or work of music can. However, it is necessary to learn to play well and only afterwards will one experience real delight.
Tigran Petrosian
First-class players lose to second-class players because second-class players sometimes play a first-class game
Siegbert Tarrasch
I’ve got no regrets about the games themselves, as frankly I’ve never been narcissistic about my play.
Alexander Grischuk 2014