People who think there's no such thing as mild, moderate or severe levels of autism. While we've established that everyone on the spectrum is different from one another, mild and severe can be useful descriptors to use for SOME of us who really ARE mild or severe.
Moderate = the most common autism that is both OR neither mild or severe.
Mild = no speech delays in childhood, articulate, ASD more invisible, come across as quirky more than challenged, often people in this group work, get married and even have children (though that's not to say all mildly autistic people can do those things but their incapabilities are more likely to be due to co-morbids such as ADHD, anxiety, depression or bipolar).
Severe = usually non-verbal, or spoke later than average in childhood, and often spoken communication in childhood wasn't articulate, their condition is more visible or obvious in their actions, behaviours and communication, may have more 'stereotypical' autism behaviours such as visibly stimming (hand-flapping or rocking). May live independently but under support from the social, may struggle more with taking part in NT society, may be more obviously 'challenged' rather than just quirky.
When I was first diagnosed at 8 years old (so young for an articulate female Aspie on the very mild end of the spectrum), I knew a 7-year-old boy with what was described as "severe autism". He was in diapers, couldn't say any words, could only shout and bark, and had aggressive meltdowns and just spent all the time in his sensory room on his own, completely shutting out the world and not wanting any other children anywhere near him. He always had his hands over his ears when near other people. I was actually a little afraid of him, and I said to my mum that I'm comparable to him because I was on the spectrum, even though I actually felt more comparable to my NT peers than I did him.
He's obviously level 3, I'm level 1. My female autistic friend is level 2. She's a bit more complex than me or the autistic boy (although I don't know him any more but I'm just going by what I had known of him). She exhibits both severe and mild autism depending on her environment. She didn't speak until she was about 8. I spoke when I was 13 months (well that's when I said my first word, then after that I just started stringing words together like the average toddler and had no delays in speech at all). Before my first birthday my parents say I would babble, point to objects or people, and hand toys to people.