Normally you might accomplish something like this as a completely separate render and pay the price in additional render time, but this can be avoided by using Custom AOVs instead since they are processed and output at the same time as your primary beauty render. In situations like this you can turn to Custom AOVs, these allow you to define your own custom render output for specific needs you may have like a custom ambient occlusion pass. There may also be times where you need to output custom data that isn't covered by an integrated AOV or wouldn't be output as a shading element of the beauty rendering process. These types of built-in non-beauty AOVs are referred to as Utility AOVs. These kinds of AOVs can be used in post to allow for much greater flexibility, like being able to add bokeh depth of field effects by making use of a Depth AOV. There are other built-in AOVs that can contain non-beauty data like depth information, motion vectors, and world position information. You can add even more control with Integrated AOVs by making use of Light Group AOVs, these can give you per-light control of your render in post. Redshift can output these shading elements isolated on their own separate AOV pass which can help with things like fast small-scale color adjustments in post without having to re-render the entire frame. These built-in AOVs are referred to as Integrated AOVs. While typically Redshift will only produce a color for each pixel of the frame you can configure it to include individual shading elements like reflections, refractions, global illumination, etc.

It refers to the different types of per-pixel information Redshift can produce.

AOV stands for 'arbitrary output variables'.

Redshift c4d