The definition of agoraphobia is a fear of being outside or otherwise being in a situation from which one either cannot escape or from which escaping would be difficult or humiliating.
Phobias are largely underreported, probably because many phobia sufferers find ways to avoid the situations to which they are phobic. The fact that agoraphobia often occurs in combination with panic disorder makes it even more difficult to track how often it occurs. Other facts about agoraphobia include that researchers estimate it occurs in less than 1% to almost 7% of the population and that it is specifically thought to be grossly underdiagnosed. There is obviously more to agoraphobia than what I have written today so in the near future I will be doing another post on this topic.