mental ray's tile-based distributed rendering is a way of sharing rendering tasks among several machines, or several processors on multi-processor machines, over a network. It uses a tile-based rendering method where each frame is broken up into segments, called tiles, which are distributed to participating machines. Each machine renders one tile at a time, until all of the frame's tiles are rendered and the frame is reassembled. By spreading the workload this way, you can decrease overall rendering time considerably.
You can also distribute frames across a network of machines using batch rendering. For more information, see Batch Rendering.
