In chess, and particularly in endgame studies, domination occurs when a player controls all movement squares of an enemy piece.
allowing 38...Qd3 – this dominates the knight: despite having six squares available to it, its capture cannot be avoided.
Normally, Black would be able to sacrifice his rook for the white bishop, leaving a drawn position (sacrificing it for a knight would be no good, since it is possible to force mate with bishop and knight), but in this case it turns out that the rook is dominated, and its capture cannot be avoided despite its freedom of movement.
Whichever Black plays, White continues with 3.Nd6 when only 3...Re5 avoids immediate loss.
At all stages the rook had wide freedom of movement, and twice it had the maximum number of fourteen squares available to it, yet it could not be saved; it was dominated.