In film terminology, throw is the distance of a movie projector from the screen. It is the distance the image is thrown onto the screen, and it has a large effect on screen size. Often in home theatre individuals lack the correct throw distance in the room but can buy a short throw lens. There are also "long throw" lenses available.
A related term, throw ratio, refers to the ratio of the distance to the screen (throw) to the screen width. A larger throw ratio corresponds to a more tightly focused optical system.