Hello,
What is circled is poor machine finish left by a dull insert in a machine tool. Just as burrs get dull from "machining" coffee beans, machine tools also dull. The poor finish is caused by excessive tool pressure and the cutter is chattering. Loading and unloading. Since these, noted by price, are produced as a commodity it is not uncommon to find a burr that the carbide insert in the cutting tool could have been changed a few parts earlier. Carbide inserts are not cheap and the machine is not making chips while down for retooling.
For those that like to have the sharpest burrs possible I find that the diamond stones work great. The "stone" I am referencing is diamond grit in electroless nickel on a steel plate bonded to a plastic body. Lap the burr under running water. You can see how much material you are taking off as the straight grind lines from the surface grinder will disappear after a few tuneups. Pay attention to the cutting edges and if you start to see light reflecting back at you a radius is starting to develop. Look straight on at a dull kitchen knife and you will see the same result. The radius reflects light back no matter the angle.

I was looking at a few pics earlier in this thread, I think, and the burrs had been grinding rocks or sand. You will note the scratches in a new burr are in a straight line as this is the path of the surface grinder. Circular scratches are caused by burr touching or material harder than the steel getting between the burrs. I have a few pics of burrs that didn't last very long with sand in the beans. These aren't my "best" worst pics. Dull TiN coated burrs are handy for seeing the radius being formed at the cutting edge.
jpboyt