Talking about non perforated brake rotors, on a VW gol, today it appeared to have 2 perfect small holes, which don't seem to align with anything. It seems to be corrosion, but the interesting fact is that they seem to be really perfect.
These are stomata (gas bubbles) in the cast iron or cast steel of your brake rotors. Stomata are usually perfectly round, but may be teardrop-shaped. They are sometimes not visible in the original casting but appear when the surface is machined or, as in your case, worn down. They are a sign of poor quality control at the foundry.
See this link on casting defects for more information.
Example of stomata in casting:
It looks like the car sat for awhile in the past and the (worn) pads developed rust. The rusting rivets on the pads probably ate those holes into the rotor. Look at all the other rotor surfaces. Brake linings can absorb moisture and cause rust on touching steel. I have seen clutch lining rusted tight against a flywheel. It is safe, but your rotors overall look poor.
Too "perfect " for corrosion. Some rotors have holes drilled in them for cooling , so it is unlikely that the depressions would cause a problem. A couple applications of the brakes will clean off the superficial rust. Although the surface looks uneven like worn pads.
What can cause perfect holes in brake rotors?
Neglect or intentional drilling by the previous owner.
Two more seem to be starting.
Overall, the rotors appear to be in poor condition. If this car has been sitting or if you just bought it from someone then it probably needs a brake job.
You should take off the wheel, remove, and inspect the brake pads.
Vehicle tyres can have pits moulded into them like this, used to show when the item is worn down to its safe limit.
However I've never seen one on car brake rotors - the edges would erode one's brake pads and they're not in a location that is easy to inspect.
