...

The surface color, usually supplied by texture maps.

Emit Color

 The The emission energy.  Non-black values represent glow.  Use this parameter with care.  Only use for low emission objects and materials.  For brighter objects, always use a PxrMeshLight

Specular Reflection

Metallic

The Defines the metallic-ness (0=of your material.  0 is a dielectric, 1=metallic). whereas a value of 1 is fully metallic.  A PBR Metalness map can be used as the input.
This is a linear blend between two different models. The metallic model has no diffuse component and also has a tinted incident specular equal to the base color.

...

A concession for artistic control that tints incident specular towards the base color. Grazing specular is still achromatic (i.e. it doesn't tint incoming light).

Roughness

Surface roughness controls both Defines the surface roughness between the diffuse and specular responses.  Again, usually, a PBR Roughness map would be used as the input to add roughness variation.

Anisotropic

The degree of anisotropy , controls the aspect ratio of the specular highlight. 0: isotropic, 1: maximally anisotropic.

...

The index of refraction of the material which controls , controlling refraction, and also the amount of specular reflection. (It also influences subsurface scattering.)

...

An additional grazing angle / forward scatter diffuse component, primarily intended for cloth.cloth 

Sheen Tint

Amount of tint sheen toward base color. At 0, the sheen is achromatic (i.e. doesn't tint incoming light).

...

Whether the surface should be considered thin or that it forms the interface to a thick material.  When set to Thin, the index of refraction is 1.0

...