From Merrimam-Webster Online:
Agoraphobia: abnormal fear of being helpless in an embarrassing or inescapable situation that is characterized especially by the avoidance of open or public places
In psychiatry, one can have panic attacks with and without agoraphobia on top. People stop going out into public places because they fear that they might have a panic attack in public.
Personally, when I'm at a place where I can spend an extensive amount of time at home reading, studying, and writing, I notice that I also start avoiding the public. This is especially odd for me to experience as I work in an industry known for public exposure: medicine. However, I am more on the introverted side of the Myers-Briggs scale, and at times, public exposure tires me out. I thought that this would qualify me as an agoraphobe, however, as I'm not actually afraid of being helpless, it doesn't count.