Wiktionary
discovered check
n. (context chess English) A situation in a game of chess where the opponent's king is put in check, not by the piece that was just moved but by one whose line of sight to the king was opened by the move.
WordNet
discovered check
n. a check on the opponent's king that is delivered by moving a piece out of the line of attack by a queen or rook or bishop
Usage examples of "discovered check".
It stood near my queen and threatened her with check, while it discovered check to my king from your bishop.
He also showed him a few common chess situations: discovered check, double check, and forks.