This is nothing more than a special form of discovered attack. The reason this move is special lies in the piece under attack. It happens to be the enemy king; thus it results in a check. Since checks are so important, this is one of your most effective tools in a chess game. The check comes from seemingly nowhere, since the piece you move does not do the checking.
Examples of Discovered Check
Here are a couple of wonderful examples of discovered check.
1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 Bg4 6. h3 Bh5 7. Qd3 Qe7.
Alarm bells should go off in White's head. The Black queen is on the same file as his king! But White sees a fork that comes with a check, and so lacks a proper sense of danger.
Here it is: a three-pronged fork on the Black king, b7-pawn, and h5-bishop.
This little pawn move threatens the queen, gets out of check, and defends the b7-pawn with a discovered defense. Of course, the bishop on h5 is still en prise. But it's nothing more than juicy bait.
There is a surprise in store for White, whose king and enemy queen are on the same e-file, along with an enemy knight.
This discovered check takes White by complete surprise. The knight does the moving, threatening the White queen along the way. But it is the Black queen that does the checking.
You may be wondering if the shielding piece can deliver a check. Of course! Any piece or pawn can deliver a check at any time during a game, provided the enemy king is within range. Discovered check refers to a situation where the long-range piece is “discovered” giving check after the shielding piece moves out of the way. But the shielding piece can deliver check in an otherwise normal discovered attack. Here is an example with White to move:
White wins the Exchange with the discovered attack 1. Nxf6+.
The discovered attack is on the rook, and the shielding piece is giving check.
1…. Bxf6 2. Bxa8 Rxa8.
Since either piece can deliver check in a double attack, one wonders whether both can do so at the same time. And in fact they can. This little bit of overkill is known as a double check.
When both pieces deliver check at the same time, the enemy is placed in an immediate quandary. Just think back to the three possible ways out of check. In a double check you cannot block the check, since you will be blocking only one of the two checks. You also can't capture the checking piece, unless you do so with the king itself, since otherwise the other checking piece would still be checking. The only way to defend against a double check is to move the king! Thus a double check often has devastating power.
Here are some examples of that most powerful weapon, the double check.
1. d4 d5 2. c4 c6 3. Nc3 Nf6 4. Nf3 Bg4 5. Ne5 Bf5 6. g3 Nbd7 7. Bg2 e6 8. 0-0 Nxe5 9. dxe5 Nd7 10. cxd5 exd5 11. e4 dxe4 12. g4 Bg6 13. Nxe4 Nxe5 14. Bf4 Nd3 15. Qe2.
White sets up a double check that is most efficient.
If Black takes the bait with 15…. Nxf4 we get 16. Nf6 checkmate. This is a checkmate even though both checking pieces are en prise. Remarkable! Furthermore, if Black wants to wait a move to take the bait, we get 15…. Bxe4 16. Bxe4 Nxf4 17. Bxc6 checkmate.
This is another checkmate while both checking pieces remain en prise.