an excessive, irrational fear of being in open or unfamiliar places, resulting in the avoidance of public situations from which escape may be difficult, such as standing in line or being in a crowd.

In DSM–IV–TR, agoraphobia may accompany panic disorder (panic disorder with agoraphobia), in which an individual experiences unexpected panic attacks, or it may occur in the absence of panic disorder (agoraphobia without history of panic disorder), when an individual fears paniclike symptoms or limited symptom attacks but has not experienced full-blown panic attacks. In DSM–5, panic disorder and agoraphobia are treated as separate entities with separate criteria; their combined presence is considered two diagnoses. See also anxiety disorder. 

American Psychological Association