Blacksmoke

I'm getting some Roush Wheels for my 06 Gt stang.
they are 18x10.
Someone told me to find out the offset .. I did.. they are 41mm.
What does this mean and mean to me?

I have heard concerns about putting 18x10's on the front of the 06GT.
How does this apply to it?
Is offset something the shop has to do to the wheel or tire like where to place it or something?
Im confused and now I'm worried that the wheels wont fit my stang or give me probs.
Im ordering directly from Roush so a shop will have to put them on.
Thanks

PS. on the roush page it says these are specificly for the 05-06 Mustang so I'd assume they are ok and will fit fine.. am I wrong?
Heres the link..
http://store.roushperformance.com/detail.aspx?ID=683
does not say they are 18x10 here but before you click on this page theres a shopping list and it says 18x10... its at the bottom right of this page..
http://store.roushperformance.com/se...?CategoryId=14

Archion

Check this link...

Wheel offset tech