Ray casting is a computer graphics technique that involves casting multiple rays from a point, and detecting the first point of impact of each ray in the world. This data can be used to render scenes or determine specific kinds of impact depending on elements such as degree of exposure. Questions with this tag deal with the calculation and implementation of this technique.
Not to be confused with ray tracing, which is a similar process except that secondary rays are cast after the first point of impact to simulate photo phenomena such as reflection. As a tradeoff for its accuracy, ray tracing is slower than ray casting.