Disorder versus Syndrome
The official term for AS in the DSM-IV-TR, the diagnostic manual of the American Psychiatric Association, is Asperger’s disorder. However, from my review of the literature, most researchers seem to use Asperger’s syndrome instead.
The word “syndrome” is more value-neutral than disorder. “Syndrome” can be taken to refer merely to a set of symptoms. However, “disorder” has the added implication that something is wrong with the person. I suspect that is why a lot of aspies, myself included, prefer AS over AD.