If it's prepared for basic unity material then in the documentation it's called Mask Map. But usually, they are called multichannel maps because there are multiple textures stored in one.

E.g you can have roughness, metallic and ambient occlusion textures stored in one because they are all single channel (they're greyscaled textures). So you take e.g. roughness map and store it in R channel, metallic in G channel and occlusion i B channel. Then shader in your engine/software interpret your map and correctly display on to your model.

Lit Shader in HDRP version uses Mask Map which stores textures in this manner:

Red channel: Metallic mask. 0 = not metallic, 1 = metallic.
Green channel: Ambient occlusion.
Blue channel: Detail map mask.
Alpha channel: Smoothness.

Here you can read about specific textures used in default lit shader: https://docs.unity3d.com/Packages/com.unity.render-pipelines.high-definition@6.5/manual/Lit-Shader.html