X-Wing

Find a digit that appears as a candidate in exactly two cells in each of two different rows, and those cells line up on the same two columns.

That digit must occupy those two columns in one of those two rows — so it can be eliminated from those columns in every other row.

The pattern works the same way rotated — two columns instead of two rows — so it's worth checking both orientations. It's also easy to false-positive on: the digit must be confined to exactly those two cells in each row, not just present in them, so a third candidate cell anywhere in either row breaks the pattern.