Change of alloy wheels

Offset is the amount or millimetres that the rim (centre) is offset from the face where the wheels touches the hub, and is usually assumed to be negative I think. This will vary as the wheel width changes, maybe have a look on the Audi website as I'd guess that there will be optional wheels on offer, and their size, width and offset might just be listed there for you to use for reference.

Be careful as A5 and A6 have same PCD and bore size but different offset to A4 B8

Good point there, "fits A3, A4, A5, A6" does seem to be a standard description!

Edit, on the subject of description, "in good condition, though if you are picky might need a slight touch-up!" - well maybe I was unlucky, but, when I went looking for some 18" 5 spokes for fitting winter tyres to, I bought a reasonably priced set of four, with roughly the above description, what I ended up with was 3-off wheels that needed refurbishing (in my mine) and 1-off wheel that looks like an alloy eating bear had had a right go at it. Also, and something that did not bother me as I was not using the tyres was the fact that all the tyres were okay to use as they were, well 3-off were punctured, two of them were very badly cracked, one had been plugged with the black stuff that quads use, and one was nearly new but a run-flat tyre - it was on the half eaten wheel. I took the hit and moved on, might have contacted the seller but got no response, so I needed to get a fourth wheel, unfortunately the only one available was brand new but at a reasonable price, so I ended up needing to get that one refurbished as well to match the other three wheels. I did understand that buying remotely is a lottery, so beware as one person's description might not quite match your one!

For what it is worth, I was VERY anti 7 spoke wheels prior to buying my S4 second hand, kind of favouring the 5 double spoke option if possible, after buying the car, I sort of got to prefer the 7 spoke over the 5 double spoke, so felt I was lucky. Though as said above, it was 5 spokes 18" I went for deliberately for winter use as they are easier to clean and you can get your hand through to clean the inside! I must admit that I did consider new 7 spoke copies in 18" for winter use, though feel I'm lucky that after looking into it, they all seemed to be okay to fit any Audi of any age - now that can not be right!