Ray Tracing works more or less in the opposite way: Rays are sent starting from the digital camera and, once they meet an intersection point, they send new rays to every light sources. These rays travel till they reach an object, where they'll bounce from countless times to any other object in the ambient bringing with them informations like color or light, until they eventually reach our eyes. In real life any light source emits a tons of rays.
Ray Tracing is a rendering technique known for years in Computer Graphics that aims to produce physically correct 3D scenes.
