CTSD Textures from Unreal 4

[deerly beloved]

Hello! I'm trying to identify a specific type of texture map (like normal maps, specular maps, that sort of stuff).
For example, Sumo_Skin_CTSD appears as so:

It's mainly pink, with a few transparent markings. Can anyone identify what it's used for?
In case it helps, here's the albedo (Sumo_Skin_A) for reference.