Wheel offset is the distance from the center of the wheel to the mounting surface (where you install the lugs).
The above picture shoes the different types of offsets.
Positive Offset
Positive Offset is easy to remember because one is pretty much always safe with positive offset. It is generally used in most factory configurations and in most wheel configurations overall. Positive offset occurs when the mounting surface is toward the street (visible) side of the centerline of the wheel.
Zero Offset
Zero Offset is when the mounting surface is perfectly even with the centerline of the wheel. This configuration is uncommon.
Negative Offset:
Negative offset is the “deep dish” style of wheel. This occurs when the mounting surface is toward the inside (not visible) side of the centerline. This configuration can cause stress on the chassis and is purely aesthetic.
Stock offset for 93-02 F-Bodies is 56 mm.
Wheel Backspacing
Wheel backspacing is the distance from the mounting surface to the backside of the rim. Measuring from the mounting surface to the rear (not visible) side of the wheel will determine backspacing. Thus, negative offset or “deep dish” wheels will almost always have low backspacing, where positive offset will produce a larger backspace.