The article covers what CaraVR render licenses are and what they are used for.
A CaraVR render license is a license which can be used only in non-interactive sessions of Nuke, to render a Nuke script containing CaraVR nodes in batch/terminal mode.
The license is mainly designed for rendering on render farm machines, where an interactive session of Nuke is not required. Similar to Nuke render licenses, CaraVR render licenses are offered at a discounted rate compared to the interactive licenses.
More information on using Nuke with a render farm can be found here: Q100104:How to set up Nuke with a render farm
To use a CaraVR render license you also need an active Nuke license available for that machine.
The reason batch/terminal mode (non-interactive sessions) requires both a Nuke and a CaraVR license is because the script you're looking to render is a Nuke script which needs an active Nuke license to be used, and when the script contains CaraVR nodes, rendering them requires a dedicated CaraVR render license.
The Nuke license used can be of any sort such as Nuke render license or regular Nuke, NukeX or NukeStudio interactive license. If you intend on using a regular Nuke interactive license when rendering in batch/terminal mode then you will need to ensure your batch command forces the interactive license usage, by using the -i batch argument.
More information on batch arguments for Nuke can be found in the Nuke Online Help here.