This is a Y-Wing.
- The cell is called pivot cell.
- The cells are called wings. Both must see the pivot cell.
All three cells (pivot + 2 wings) must each have exactly two candidates.
One of those candidates must be in both wings, but not in the pivot cell. Here the common candidate is the 3.
For this example, there are two possible outcomes:
Since there must be a 3 in one of those two cells, we know that all cells that see those two cells cannot hold a 3.
The cells are seen by both wings, so we can eliminate the common candidate (3) from them.
Another way to look at it
If any of the 3 were true...
... then that would leave only one candidate in each wing...
... and the pivot cell would have no candidates left, and therefore no solution.
Spread over four boxes
In case the pivot cell is not in the same box as a wing, the Y-Wing spreads over four boxes.
In this case, there is only one cell that both wings see. ()