Applied Behavior Analysis (ABA): A style of teaching which uses a series of trials to shape a desired behavior or response. Skills are broken down into their simplest components and then taught to the individual through a system of reinforcement.

Asperger’s Syndrome (AS): A developmental disorder on the autism spectrum defined by impairments in communication and social development and by repetitive interests and behaviors. Unlike typical autism, individuals with Asperger’s Syndrome have no significant delay in language and cognitive development.
 
Autism: A spectrum of developmental disability disorders characterized by deficits in social interaction and communication, and unusual and repetitive behavior.

Autistic Disorder: Individuals with Autistic Disorder have a moderate to severe range of communication, socialization, and restrictive and repetitive behavior.

Autistic/Autism Spectrum Disorders: A term that encompasses autism and similar disorders. More specifically, the following five disorders listed in the DSM-IV: Autistic Disorder, Asperger’s Disorder, Pervasive Developmental Disorder - Not Otherwise Specified, Childhood Disintegrative Disorder, and Retts Disorder.

Childhood Disintegrative Disorder: Childhood Disintegrative Disorder, an extremely rare disorder, is a clearly apparent regression in multiple areas of functioning (such as the ability to move, bladder and bowel control, and social and language skills) following a period of  2 years of apparently normal development.