Autism spectrum disorder (ASD) is a neurological and developmental disorder that begins early in childhood and lasts throughout a person’s life. It affects how a person acts and interacts with others, communicates, and learns. It includes what used to be known as Asperger syndrome and pervasive developmental disorders.
Merriam-Webster Online Dictionary
autism spectrum disorder (noun)any of a group of developmental disorders (as autism and Asperger's syndrome) marked by impairments in the ability to communicate and interact socially and by the presence of repetitive behaviors or restricted interests - called also autistic spectrum disorder pervasive developmental disorder