Asperger syndrome by DSM-IV (diagnostic manual) was part of that group of conditions related to autism onset in the development which are called neurodevelopment disorders. By DSM-5 (diagnostic manual), this syndrome has been excluded, and it is diagnosed as Autism spectrum disorder or Disorder of social pragmatic communication.
From DSM5: Individuals with a consolidated DSM-IV diagnosis of autistic disorder, asperger’s disorder or pervasive developmental disorder should receive the diagnosis of Autism Spectrum Disorder. Individuals who have severe social communication deficits, but whose symptoms do not meet the autism criteria should be evaluated for pragmatic social communication disorder.
To understand what Asperger’s syndrome is, you must first understand what autism is, more correct called Autism spectrum.