XY-Wing

XY-Wing is a more advanced strategy that commonly appears in my more difficult puzzles starting with the Tough level. In my experience, this occurs more than the X-Wing, but can be a bit more difficult to spot.

This is essentially a short forcing chain that begins with a square that contains just two candidates (X,Y). If the cell is X, another cell sharing the same container is forced to Z (row 2 here). If the cell is Y, another cell sharing a different container is forced to Z (column 2 here). Any other cell connected to both of the Z cells cannot itself be Z, as in the highlighted cell in r5c5.

Here are two other configurations of XY-Wing. In this case the interaction is between a row and a block. These ones are especially hard to spot, I find.

Notice that the above two configurations are actually the same conditions, so we can combine them as follows, resulting in a big payout!

This next puzzle contains an XY-Wing in the highlighted cells.

Which number (of 2,5,7) is the Z?

Where are the other Zs we can erase? I see two of them.