Check

When a player moves a piece to a position where an opponent's king is directly threatened, that king is said to be in check. The player putting the opponent's king in check must announce, "Check." The player with a king in check must respond when their turn comes by escaping check.

There are three ways to escape check:
• capture the checking piece
• block the checking piece
• move the king out of check

Check Pending

When a player checks the opponent on their right, the opponent on their left gets to move before the checked player can respond. That opponent might interfere with the check or might exploit it. This is called check pending.
(See below.)

Black bishop captures white bishop and puts white king in check
A black bishop puts the white king in check. It is Red's turn. Red could interfere by capturing the checking piece with the Red bishop, putting White in check by Red, or Red could exploit the situation by capturing a white knight with the red queen. Either way, White will have to respond to being in check.

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Double Check

There are two types of double check. The first type is when a king is in check by two pieces at once. The second is when one piece puts two kings in check with a single move. The figure below illustrates the second type.

Black bishop captures white bishop and puts white king in check
The black queen puts both opponents in check with a single move.