Can someone explain the
x-ray tactical motif? I have looked at this example, but I still don't understand it fully. If you can provide other examples, that would be great too.
Basically, if a defending piece of your opponent has one of your pieces with the same movement "behind" it, then it's not really defending anything, as your piece standing behind also "attacks" what you want to capture through that defending piece of your opponent's.
In the following exampe, the
♞g6 is x-ray-attacked by the
♖b6, through the
♜d6, so once the other rook takes it, it is defended through the black rook by the
♖b6 (and the knight is lost).
[FEN "7k/4p3/1R1r2n1/P7/6R1/8/8/7K w - - 1 1"] 1. Rxg6
[Title "your example"] [fen "4r2k/Bb1n2pp/2q1r3/1R1Qpp2/2P5/5P2/P4KPP/4RB2 w - - 0 1"] 1. Rxb7 Qxb7 2. Qxb7
when R x b7, your Queen on d5 is guarding the rook, even though it doesn't look like it. That's because if Black plays Q (c6) takes b7, your Q (d5) can take it back.
The reason "it doesn't look like it" is because the Black Q on c6 appears to be blocking the way to b7. That is, until the Black Q herself moves to b7. Thus, your Q d5 has "xray" power to b7 through the Black Q on c6.
Basically, an x-ray attack is one where, even if one of your long range piece (queen, bishop, rook) is being blocked by another piece, then you should still look at the squares that your blocked piece can attack through the piece that's blocking it. Here's an example.
[fen "r1Q2b1r/1p1R1pp1/p1b2k2/8/2q2Np1/2P1B2P/PP3P2/2K4R w - - 0 1"] 1. Bd4+ Kg5 2. Rd5+ Qxd5 3. Qxg4+ Kh6 4. Qh4+ Qh5 5. Qxh5++
Here, the queen's power is unleashed on the poor g4 pawn after the rook moves after which his majesty is thrown off the board. Always look out for tricks like this, and the one in the link that you posted in the question. An x-ray attack can be used simultaneously with discovered attack. But the basic idea is that one of your pieces "sees" through another.