Appropriate for simulating metallic surface finishes accurately. The appropriate values for various conductors (metals) can be obtained from published data in handbooks of optical constants.
The surface color, often supplied by texture maps.
Specularity is the correct term for reflection. Normally all surfaces have some element of incident reflection and this setting is usually accompanied by a Roughness setting (in the Standard material this accompanying setting is called Glossiness and works in the opposite direction - 100 % Glossiness is the same as 0 % Roughness).
This setting is usually paired with Specularity and defines how tight the reflection will be. A high roughness will mean that the surface might be reflective but the reflection will be diffused and unrecognizable.
Anisotropy is a bias in the direction of lighting a surface. At 0 % a surface is isotropic, meaning there's no bias. As you approach 100 % your surface will become maximally anisotropic. Some degree of Roughness is necessary for anisotropy to be visible, and the amount tells the anisotropic highlight how far to "spread".
Anisotropy requires that there is a Projection node input otherwise you will get strange polygonal shapes in the render.
Left: Anisotropy at 100 %, Rotation at 15 %, Roughness at 30 %. Right: No Projection
This determines the angular rotation for your anisotropic highlights. At 0 % the rotation will follow the curve of your object and at 50 % will be perpendicular to it.
Bump Height (Scalar)
Specifies the bump height or “amplitude” of the Bump directional vectors.