He means they were turned on a lathe to remove any grooves and
possibly improve the flatness of the surface. I think some shops can
do it on the car (since labor would be the major cxost of this).
A new rotor is $60 from volvoparts.com. It is common to replace
the rotors rather then turn them (rotors are good for about two
sets of brake pads which is roughlt 60-70K miles).

I think you should search (using the search below) on brake problems
and shimmy. USe something like:

brake shimmy rear rotor front

since this is a common problem. Often traced to the rear brakes. You
might be able to more closely match your symptoms to what others have
reported to help narrow it down.

Typing this in at google.com also found a lot:

volvo 850 rear front brakes vibration