Doug said 'The Microsurface/ Roughness or Smoothness (in Substance Painter it refers to as Glossiness - which I'm not sure of anymore - but that is another thread) texture (Alpha Channel) would be R177, G176, B177.'
In Substance painter it refers to it as both roughness and glossiness, you have the choice of either, roughness being from the metallic workflow and Glossiness being from the Specular workflow. Roughness is an inverted glossiness and visa versa. I think microsurface is the general term but its often referred to as Gloss, Smoothness or Roughness. I think Smoothness is more a game engine term, likes of P3d or Unity use it, whereas the ill-fated Flight Sim world (which used both workflows) used roughness and microsurface as its naming (Roughness when working with a Metallic workflow and microsurface instead of Glossiness for Specular workflow).
Glossiness and Roughness is more a workflow naming. Note:Even in this image the Albedo is called the Base Colour
No matter what the naming its still just the same thing, Glossiness/smoothness/roughness/microsurface all mean the same thing, just depends which workflow youre working on, or in the case of P3d it seems to be Metallic workflow with a Specular Glossiness instead of a Roughness. In X-plane it is referred to as a Roughness but watching an official tutorial it is in fact a Glossiness map???.......gets a bit confusing keeping up with it.......
That's my findings on that anyhow....
Stevo