Usually this refers to people who are
autistic, but manage to function just fine in society, in terms of
communicating,
holding a job, and so forth. They have all the symptoms of
autism, just not the severity of
disconnection. The person usually cited is
Temple Grandin who has written from the point of view of the high functioning autistic person about her childhood and career.
My son is very likely high functioning autistic. He has just turned four. He has not learned to speak as well as most three-year-olds, but he is very intelligent nevertheless, especially in academic skills.
It's tough being the parent of a child with this kind of problem, though not nearly as hard as it is for parents with autistic children who can't speak or care for themselves. The hard thing is deciding when to treat them just like any other kid and when to give them special help. Sometimes they need extras, but you want them to be able to do it all on their own when they're grownups.