Dolly: This is the process of moving a camera. To move a camera forward is to dolly in, and to move a camera backwards is to dolly out.
Zoom: This term is often erroneously used interchangeably with dolly. It is the process of changing the size of a camera's angle of view, without moving the camera. To decrease the angle of view is to zoom in, which makes everything appear universally larger. To increase the angle of view is to zoom out, which makes everything appear universally smaller. A vert - solution causes a zoom in. Because it is often assumed that dolly out and zoom out are the same thing, it is also often assumed that a dolly out can cancel out the zooming in of a vert - game. Both of these assumptions are incorrect.
For the purpose of comparisons, this article will use screenshots from the game Heavy Metal FAKK2. It is a third person action game where both the dolly level and zoom level are independently controllable. Dolly level is controlled by the var cg_cameradist, which defaults at 120. Zoom level is controlled by fov, which defaults at 90.