This is commonly expressed as the ET value, where ET (Eiinpresstiefe) is the distance from the dead center of the wheel to the contact face against the hub. All rims have an offset of some kind; ET 35 is pretty normal, and means that the contact face is offset 35 mm outwards from center. The correct Norwegian term is innpressing, btw...

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Note added at 1 hr (2007-11-19 19:12:20 GMT)
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The rim offset is a highly underestimated factor in determining a vehicle's steering characteristics. A fine-tuned car like a Beemer may turn really bitchy if a replacement set of wheels changes the ET value from 32 to say, 48. What used to be a self-stabilising negative scrub radius suddenly becomes a twitchy, steer-towards-the-traction setup, which at best keeps the driver awake and alert.

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Note added at 1 hr (2007-11-19 19:17:32 GMT)
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The 'Min. innpress' value in a vehicle registration document defines the minimum rim offset that is allowed. The lack of a maximum offset figure is proof indeed of the vehicle authorities' lack of understanding in this matter. Too much offset is just as dangerous as too little offset.