Which property is true for the diagonals of every rhombus but is NOT true, in general, for the diagonals of a rectangle?

Both shapes are parallelograms, so in both the diagonals bisect each other and both diagonals lie inside the figure. The perpendicularity is special to the rhombus: its diagonals meet at 90°, while a rectangle's diagonals meet at 90° only when it happens to be a square. Equal length is the reverse case — true for every rectangle but false for a rhombus that is not a square.