In general, i believe physicians use the terms ADD and ADHD synonymously. Most now call it just ADHD, probably because 1) They don't really know the difference themselves 2) that's what TV and the prescription drug companies tell them to call it.
That being said, there are still different sub-types of ADD/ADHD: Inattentive and Hyperactive.
Take a look at this article to get a closer look at the differences:
The Difference between ADD and ADHDTwo additional articles on adult ADD and ADHD:
What does ADD feel like?What does ADHD feel like?Hope this helps.
Stefford.