A digit in two rows aligned on two columns (or vice versa). expert
Digit 9 in columns 4/7 fits only at the marked positions, which line up on rows 4/5, one per line, so erase it from R4C1, R4C2.
When a digit's candidates in two rows fall on the same two columns, they form a rectangle: the digit must sit on two opposite corners. Erase it from the rest of those columns (or swap rows and columns).