Hey Vata,
It’s a general term for 3D work which implies that someone is painting the vertices of a model with certain colors inside of the engine or 3d software. It is used in animation, fx, characters, and environments.
For purposes of my Procedural Nature Pack, there is a vertex painting tool inside of UE4 that I used and setup to allow people to paint moss onto rocks. It’s essentially the same tool used to paint different materials onto different parts of the landscape. Here is a quick video of someone doing some vertex painting in Unreal. Hope that helps!
[video]https://youtu.be/p6O4AgSwTmQ?t=4m[/video]