The offset of any billet wheel is the distance from its hub mounting surface to the centerline of the wheel.
The hub mounting surface is even with the centerline of the forged billet wheel.
The hub mounting surface is located in the front half of the billet wheel closer to the wheel face. This tucks the entire wheel in toward the brakes and vehicle suspension. Positive offset wheels are generally found on front-wheel drive cars and newer rear-wheel drive cars.
The hub mounting surface is located in the back half of the billet wheel closer to the back lip flange. This moves the wheel out away from the vehicle brakes and suspension. "Deep dish" forged billet wheels and forged billet wheels for lifted trucks are typically a negative offset.