An out of round tire is one that has been defectively manufactured in an oval shape. AMG had lots of problems with out of round 16.5" GSA's in the past. The one piece steel wheels had a lot of quality control problems with run-out. Run-out is when the wheel is doesn't run true and wobbles from side to side. There are a lot of bent wheels out there from hard off-roading. There have been a number of problems with the 2 piece runflats coming loose in the wheel causing out of balance problems.
It is important to watch where you are going not just to avoid a flat tire, but because certain hazards can damage your vehicle’s wheels. If you have accidentally hit curbs more than once or driven too fast over speed bumps, it could bend the wheel. The same can be said for driving over potholes in the road. If you make a habit of driving a little too close to parking space bumpers and hitting them with your front wheels, you might notice that those wheels are more out of alignment than the back wheels. This is a good indication of the cause of your wheels being out of balance.