the wheel offset is the value from the center of your wheel to the mounting surface point of the wheel. If the mounting surface point of the wheel is more to the outside of the wheel (towards the front spoke surface), it is called a positive offset (hence, more positive values means you will get your wheels inside the body of your car).

if the fitting point of the wheel is more to the inside of the wheel (towards the rear lip surface), it is called a negative offset (where you will get wheels outside your car body).

as long as the wheels do not hit the calipers; and/or will not rub the inner fender when turning your steering, you're good to go.

 

it shall be noted, as well, that typically FWD cars, with their requisite cv-joint housings and half-shafts, will have the hubs/rotors/cals poking farther out into the fender wells. this necessitates higher-offset wheels (about 30 to 35mm). these wheels will most often have a very shallow lip, if any, and run the spokes on or very near the front surface of the wheel.

conversely, RWD and wide-body cars can run typically lower offset wheels, those with a fatter lip or "deep dish." this is often why you see drift cars and/or GTRs with these awesome looking wheels with the fat lip --rwd.