Throw Ratio
The relationship between a projector's distance from the screen and the resulting image width, expressed as a decimal. A 0.9 throw ratio means the projector needs to be 9 feet away to produce a 10-foot-wide image; a 1.5 throw ratio needs 15 feet for the same image.
Lower throw ratios are better for golf simulators because the projector mounts closer to the screen, casting smaller shadows during the swing. Anything under 1.0 is "short throw"; under 0.4 is "ultra short throw" and mounts essentially against the wall.
When sizing a build, measure throw ratio against the depth of your room and the height of your ceiling — a 0.5 throw ratio sounds appealing until you realize it requires the projector to be mounted directly above the hitting mat.