Quick answer: acne marks or acne scars?
If the skin is flat but discoloured, it is more likely to be an acne mark.
If the skin has pits, dents, depressions or uneven texture, it is more likely to be an acne scar.
Some people have both. For example, a person may have brown post-acne marks along with pitted acne scars and active acne.
That is why the first step is to separate:
The treatment plan should be based on what is actually present.