Great questions! None of those are clinical terms. “Highly functioning” is an informal term used frequently by doctors, parents, and the like — and it is demeaning. The assumption, latent in the term, is that if someone works, makes money, pays bills, etc, they have more worth — which must mean they have less Autism. It’s not an accurate term, either — a person can be really “capable” in one area of life and totally not in another — I’m a great example of this, I think. So “mild” Autism itself isn’t really a thing, either. People talk about Autism like it’s a single spectrum, but really, every single Autistic trait is itself a spectrum — you can be high, low, or medium on sensory sensitivity, high, low, or medium in discomfort with eye contact, high/low/medium on executive functioning, and on and on.