Agoraphobia is an anxiety disorder characterized by fear of situations in which one might be trapped and unable to get help, especially in the event of a panic attack. Agoraphobics may avoid crowds, enclosed spaces (such as elevators and buses), or large open spaces. Like other anxiety disorders, the first line of treatment for agoraphobia is exposure therapy. In exposure therapy, the patient is exposed, either in vivo (i.e., in person) or imaginally, to the situation or object that he or she fears. Repeated exposure allows the agoraphobic patient to learn that his or her fears are unfounded.
From the Greek "fear of the marketplace"
Abnormal Psychology, Rosenhan & Seligman, 1984