Render Elements are a way to break out renders into their component parts such as diffuse color, reflections, shadows, mattes, etc. This gives fine control over the final image when using compositing or image editing applications when re-assembling the final image from its component elements.

Render Elements are generated at render time based on the ones you choose before rendering. Most render elements have parameters that can be set to customize the render element or its later use in compositing software. 

They are accessible from the V-Ray Settings menu.

Beauty

The Beauty Render Elements are the primary render elements that form V-Ray's pre-composited final render Beauty (RGB_Color) image.

Filters

Shows only the selected set of channels in the render, disregarding any backgrounds, textures, etc.

Masks

Provides a variety of Render Elements to be used as masks in the compositing process.

LightMix

Provides adjustment control to the lights in the scene from inside the New V-Ray Frame Buffer.

Cryptomatte

Uses the Cryptomatte convention by Psypop to encode mattes (Node Names, Material names) into multichannel OpenEXRs.

Coordinates

The Coordinates Render Elements are based on the scene geometry that serve different purposes.

Light Select

Stores direct lighting information from user-selected lights in the scene; can also be limited to the light's raw, diffuse, or specular contribution.

Utilities

This group of Render Elements can be used for troubleshooting purposes.

Custom

You can add any of the render channels again from the Custom option, allowing you to use it with a different setup.