Deflection
Deflection is forcing a defending piece off the square or line where it was doing useful work.
A check or a capture on a new square can pull the defender away. Once it has left, the original target is no longer guarded.
Ra8+ forces the queen on f7 to interpose on e8 or f8. Either way it leaves f7, and White’s queen can use that file. The rook did not win material by itself; it moved the defender.
Deflection is close to decoy. The difference is the goal: deflection cares about the square the piece left, not the square it landed on.