Imagine you have pictures of some real-life object from many angles, and want to turn it into a virtual 3d object (for a web shop, or for use in a computer game, or whatever). Traditional methods try to reconstruct the geometry, but have a couple of problems in more complex situations. NeRFs are a quite new approach that tries to accomplish the same task by training a neural net that essentially allows you to query the color of each point in space (also accounting for the direction you are viewing from). This works great (and works from as few as two source images), but it's slow, and rendering the result was even slower.

This paper introduces a way to render NeRFs at reasonable speed. Still not stellar, but quick enough to make NeRFs useful for many use cases.