The autism spectrum, also called autism spectrum disorders (ASD)
or autism spectrum conditions (ASC),
with the word autistic sometimes replacing autism,
is a spectrum of psychological conditions characterized
by widespread abnormalities of social interactions and communication, as well as
severely restricted interests and highly repetitive behavior.

Autism forms the core of the autism spectrum disorders.
Asperger syndrome is closest to autism in signs and likely causes;[2]
unlike autism, people with Asperger syndrome have no significant delay
in language development.[3] PDD-NOS is diagnosed when the criteria
are not met for a more specific disorder. Some sources also include
Rett syndrome and childhood disintegrative disorder, which share several
signs with autism but may have unrelated causes; other sources combine
ASD with these two conditions into the pervasive developmental disorders.[2][4]

The terminology of autism can be bewildering. Autism, Asperger syndrome
and PDD-NOS are sometimes called the autistic disorders instead of ASD,[5]
whereas autism itself is often called autistic disorder, childhood autism, or
infantile autism.[6] Although the older term pervasive developmental disorder
and the newer term autism spectrum disorder largely or entirely overlap,[4]
the former was intended to describe a specific set of diagnostic labels, whereas
the latter refers to a postulated spectrum disorder linking various conditions.
[7] ASD, in turn, is a subset of the broader autism phenotype (BAP),
which describes individuals who may not have ASD but do have autistic-like
traits, such as avoiding eye contact