Work is equal to the force applied to an object multiplied by the distance it had travelled. This is work as long as the force and the direction of the distance in going in the same direction.
It is work because you're applying a force on an object to move it.
For example, work is done when you push a box across the floor, but work is not done when you lift the box up and then walk it across the room. This is because the force on the box is upwards since you're lifting it and the direction of the distance is left or right so the directions are not the same.
