Wheel diameter value is in Inches, it is the diameter of the wheel without the tire.
Wheel width value is in Inches, it is the width of the section between the mounting flanges on the wheel.
Offset has an ET (Einpress Tiefe) value in millimetres (mm) which indicates the distance between the mounting surface and the geometric centre of the wheel.
Often displayed as:
17 x 7 ET 48