* Displacement is the change in position of an object. It's a vector quantity, meaning it has both magnitude (how much) and direction.

* When the ball is thrown upwards and comes back down to the thrower, it ends up at the same position it started.

* Since there is no overall change in position, the displacement is zero.

Important Note: While the displacement is zero, the distance traveled by the ball is not. The ball travels a certain distance upwards and then the same distance downwards, making the total distance traveled non-zero.