Swordfish

A swordfish looks at three rows where a digit's candidates are confined to the same three columns overall (each row has 2–3 of those candidates, never elsewhere).

That's enough to guarantee the digit occupies those three columns across those three rows, so it can be eliminated from those columns in every other row.

A common misreading is assuming every row needs all three columns filled with the candidate — a row can use as few as two of the three, as long as none of the three rows strays into a fourth column. Solvers usually reach for a swordfish only after confirming no simpler X-Wing accounts for the same digit.