A professor is explaining autism spectrum disorders to his students. he is most likely to state that

The professor should probably introduce his students that Autism refers to a general term which is used o describe brain development disorders which are characterized in different degrees, like difficulty in interacting socially with other people, not making eye contact, verbal or non verbal communication errors etc.

He should probably tell them that until recent years there were considered various forms of Autism but now all of them are known as "called "autism spectrum disorders".