Different organizations have slightly varying definitions, which depend on their point of view or emphasis. Here are a few basic ones, from the Centers for Disease Control and Prevention (CDC), National Institute of Mental Health (NIMH), and Mayo Clinic, followed by a short list of other sources to explore.

A Definition from the Centers for Disease Control and Prevention

Autism spectrum disorders (ASDs) are a group of developmental disabilities that can cause significant social, communication and behavioral challenges. People with ASDs handle information in their brain differently than other people.

ASDs are "spectrum disorders." That means ASDs affect each person in different ways, and can range from very mild to severe. People with ASDs share some similar symptoms, such as problems with social interaction. But there are differences in when the symptoms start, how severe they are, and the exact nature of the symptoms.

There are three different types of ASDs:

  1. Autistic Disorder (also called "classic" autism)

    This is what most people think of when hearing the word "autism." People with autistic disorder usually have significant language delays, social and communication challenges, and unusual behaviors and interests. Many people with autistic disorder also have intellectual disability.

  2. Asperger Syndrome

    People with Asperger syndrome usually have some milder symptoms of autistic disorder. They might have social challenges and unusual behaviors and interests. However, they typically do not have problems with language or intellectual disability.

  3. Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS; also called "atypical autism")

    People who meet some of the criteria for autistic disorder or Asperger syndrome, but not all, may be diagnosed with PDD-NOS. People with PDD-NOS usually have fewer and milder symptoms than those with autistic disorder. The symptoms might cause only social and communication challenges.

What is Autism?

CDC What is Autism? Video on Autism Spectrum Disorder

Reference

Definition from the National Institute of Mental Health

The National Institute of Mental Health definition has other information. Note that this definition emphasizes children. Adults have Autism Spectrum Disorders too, of course. Autism affects people of all kinds across the entire life span.

What Are the Autism Spectrum Disorders?

All children with Autism Spectrum Disorder (ASD) demonstrate deficits in

  1. social interaction,
  2. verbal and nonverbal communication, and
  3. repetitive behaviors or interests.

In addition, they will often have unusual responses to sensory experiences, such as certain sounds or the way objects look. Each of these symptoms runs the gamut from mild to severe. They will present in each individual child differently. For instance, a child may have little trouble learning to read but exhibit extremely poor social interaction. Each child will display communication, social, and behavioral patterns that are individual but fit into the overall diagnosis of ASD.

Reference

Definition from the Mayo Clinic

By Mayo Clinic staff

Autism is one of a group of serious developmental problems called autism spectrum disorders (ASD) that appear in early childhood - usually before age 3. Though symptoms and severity vary, all autism disorders affect a child's ability to communicate and interact with others.

The number of children diagnosed with autism appears to be rising. It's not clear whether this is due to better detection and reporting of autism, a real increase in the number of cases, or both.

While there is no cure for autism, intensive, early treatment can make a big difference in the lives of many children with the disorder.

Reference

Mayo Clinic Autism Definition (http://www.mayoclinic.com/health/autism/DS00348)

Other Resources and Links