What is "tiled" raytracing? I've seen mention of tiled raytracing, but haven't been able to find much on google about it.

Can anyone explain what it is and how it works?
Tiled raytracing is a way of speeding up rendering.  Instead of rendering pixels on a row-by-row basis down the entire image, you render them in 2D groups (say, 32x32 tiles).  Since adjacent rays tend to intersect the same objects, this improves the cache hit rate at the CPU level.

At a smaller scale, tiling at the 2x2 level lets you use SSE/AVX/etc to compute four rays with a single CPU instruction, further speeding things up.