The mental ray® for Maya® renderer can render using a feature called Global Illumination. Global Illumination simulates the effect of all lighting and inter-reflection in the scene, whether the items are lit directly by a light source or indirectly illuminated by other objects (and diffuse sources of illumination in the scene).
For example, when a photographer lights an object in a studio, some of the lighting for the object in the final image comes directly from the lights that are used, while additional illumination comes from objects that are placed near the subject to act as light reflectors. These are referred to as fill cards. Light bounces off the fill cards, indirectly lighting nearby objects with a secondary source of diffuse light. The color of the fill card colors the light that gets reflected onto the object. The final illumination of the object comes from this combination of multiple sources (direct light, specular reflections, and diffuse light).