Autism is a pervasive developmental disorder which affects social and communication skills and, to a greater or lesser degree, motor and language skills.

It is such a broad diagnosis that it can include people with high IQ’s and mental retardation - and people with autism can be chatty or silent, affectionate or cold, methodical or disorganized. So, what exactly is an autism spectrum disorder? These articles are a good place to get the basics:

What Is Autism?