\begin{definition}[Definition:Chess/Rules/In Check]
Uniquely among the chess pieces the king may not legally move into a square which is under attack by a piece of the opposite colour.
That is, a king may not be moved so as to be placed under attack.
If player $a$ moves a piece so as to place the king of player $b$ under attack, then player $b$ is said to be '''in check'''.
Player $a$ is then obliged to say '''"Check."'''
Player $b$ must make a move so that his or her king is no longer under attack.
Such a move by player $b$ is known as '''getting out of check'''.
Category:Definitions/Chess
\end{definition}