Hi Jaydude4d,
This is a more extended discussion, or perhaps as short as this one: It is all about the surface and light qualities.
Well, this is not really helping, of course.
BSDF is short for Bidirectional Scattering Distribution Function. It is the idea to mathematically define the way light is treaded in conjunction with surfaces.
This is also too short, the WIKI site might be more precise:
https://en.wikipedia.org/wiki/Bidirectional_scattering_distribution_function
The answer to the specific node is here:
https://help.maxon.net/us/index.html#NET_MAXON_RENDER_NODE_BSDF-NET_MAXON_NODE_BASE_GROUP_INPUTS
All the best