Double check
From Conservapedia
Double check is an unusual and very effective way in chess to attack an opponent's king, such that it is placed in check by two pieces rather than one. Chess notation sometimes adds a "++" (which can also connote checkmate), or may be silent about the doubling of the check.
This is a type of "discovered attack" that results when moving a piece opens an attack by an underlying piece whose attack was previously shielded.
As Garry Kasparov explains:
| “ | especially powerful form of discovered attack. As in other forms of discovered attack, moving one piece reveals an attack from another piece. In this case, though, both the piece being moved and the piece being uncovered are used to attack the king.[1] | ” |
Interestingly, it is only possible in conventional chess for a king to be in check by a maximum of two pieces.
