Phase 1 Clio has a 36 offset, or at least a 16v does. The offset is a measure of how far away the flat mounting face of the wheel is from the centreline (half way between the outer and inner edge of the rim). If you had a wheel with its mounting face exactly half way between the outer and inner edge of the rim it would have a zero offset. If you got that wheel and put it on a milling machine and started to take metal off the mounting face so it got deeper and deeper into the wheel, you would be increasing the offset. On a car, the effect of this would be that the wheel would move inwards. So the more offset you have the more in the wheels are. The less offset you have, the more out the wheels are, which is why sometimes if you get a wheel with the offset too low, your wheels will stick out past the wheelarches and fail the MOT! You can even have negative offset, denoted by a - sign before the number, eg. -25. This would mean the mounting face is actually 25mm closer to the inner edge of the wheel from the centreline. Negative offset setups are quite rare on road cars, I would have thought because the further out the wheels are from the suspension, the harder the suspension has to work and more prone to failure it will be.
