Step-by-step explanation:
Displacement is a difference between an initial value and a final value, not factoring in any changes that happen in between. For example you let an object of a certain volume sink to the bottom of a container of water, the water level will be displaced, or changed, by exactly the volume of that object.
Example: A marble with volume of 3 cm³ is dropped into a graduated cyllinder with 10 mL of water. The water level rises to the 13 mL mark, so the displacement of the water by the marble is exactly 3 mL.
This doesn't just apply to a change in volume: If I move a box 3 meters along an axis in the positive direction, we say its displacement along that axis is 3 meters. If I moved it in the negative direction the same distance, the displacement would be -3 meters.