The Beauty AOVs are split into two categories, Beauty - Surfaces and Beauty - Volumes. 

Beauty - Surfaces

These AOVs are RGB passes of various surface shading attributes.

Denoise Albedo AOV - Outputs the denoised albedo information. 

Denoise Normal AOV - Outputs the denoised scene normal information.

Diffuse AOV -  Outputs only the diffuse component of the scene.

Diffuse Direct AOV - Outputs only the single bounce direct of the scene. No indirect contribution.

Diffuse Filter (Beauty) AOV - Outputs only the non-shaded view of the scene, which are flat regions of the base color or albedo of each material.

Diffuse Indirect AOV - Outputs only indirectly-shaded diffuse pixels within the scene.

Emission AOV - Outputs any light source or light-contributing pixels of the scene.

Environment (unoccluded) AOV - Similar to the existing Environment render AOV but only contains the parts of the environment that are directly visible to the camera. This can be used for more accurate compositing for pixels that are partially covered by geometry, where the color of the environment in the covered part is significantly different to the color in the uncovered part.

Environment AOV - Outputs any visible portion of the environment in the scene.

Reflection AOV - Outputs only those pixels that receive reflections in the scene.

Reflection Direct AOV - Outputs only those pixels that are directly reflecting light. No bounce reflections are included in this AOV.

Reflection Filter (Beauty) AOV - Outputs only those pixels that are receiving reflections in the scene. Output is grayscale. (check this)

Reflection Indirect AOV - Outputs only those pixels receiving indirect reflections.

Refraction AOV - Outputs any pixels receiving refractions in the scene.

Refraction Filter (Beauty) AOV - Outputs only the unshaded pixels receiving refractions in the scene.

Subsurface Scattering AOV - Outputs only the pixels illuminated by sub-surface scattering.

Transmission AOV - Outputs only those pixels that are transmitting light.

Transmission Filter (Beauty) AOV -  Outputs only unshaded pixels transmitting light in the scene.

Beauty - Volumes

These are AOVS that pertain to volume information and shading.

Volume AOV - The volume AOV contains all samples that are scattered in a volume.

Volume Emission AOV - The volume emission AOV contains all of the samples where the camera ray hit a volume emitter.

Volume Mask AOV - The volume mask AOV contains absorption color and the contribution amount of a volume sample. This is a multiplication AOV. To composite volume AOVs, a typical formula would be: (allOtherBeautyPasses)*volume mask + volume + volume emission.

Volume Z-Depth Back AOV - The volume z-depth back AOV contains the back depth of all volume samples.

Volume Z-Depth Front AOV - The volume z-depth front AOV contains the front depth of all volume samples.

Beauty - Other

Gaussian Splat AOV - Outputs only the Gaussian splat aspects of a scene and includes relighting effects as seen in the beauty pass.