The Autism Spectrum is a mental axes which determines one's severity of autism of an individual. It covers many layers of autism, but can be placed into three general groupings. While this is not to be confused with the autism ideology spectrum however most often than not they are greatly related in where an ideology would be placed in the ideological autism spectrum.
Level 1 (Thunbergian)
Level 1 Autism, or High-Functioning Autism, which also includes Asperger's Syndrome (disputedly, Cyanism and CWC Model do not consider it to be part of the autism spectrum) and Pervasive Developmental Disorder (PDD), is the least severe form of Autism. People in this category display signs of social impairment.
Level 2 (Grandinian)
Level 2 Autism is the second most severe form of Autism. They are characterized by need for substantial support, and their communication skills and repetitive behavior is still obvious to the casual observer, even with support in place.
Level 3 (Chris-Chanian)
Level 3 Autism, Low-Functioning Autism or Classic Autism, is the most severe form of Autism. Their communication skills and repetitive behavior severely impair daily life. This video should give you an idea of what this is.