The Render Properties' Buffers tab shows available buffers organized into groups. They are:
These are buffers which the render engine itself makes available.
These are buffers which shading system elements, such as the Material nodes and Shading Models, provide.
This group contains any existing Light Buffer Groups. Each of the groups will contain its own set of the buffers which are known as "Direct" buffers, since this data can be broken out into a Light Buffer Group specific buffer.
Custom Buffers can be created to fulfill specific purposes, like breaking out surfaces of an object. They are stored with surfacing, so loading an object that has a Custom Buffer will add that buffer to the system.
Buffers can have a large amount of data in them, represented by different colors. The means of displaying these colors depends on the format output.
The Compositing Buffer Export Image Filter has currently been moved to the LightWave Legacy plugin archive while changes are made to LightWave's buffer system.