A phobia is an intense anxiety about one or more specific things or situations. Most of us have some triggers for revulsion or avoidance, like mice, public speaking, or leaning over a balcony in a high building, but these are fairly normal. Phobias, on the other hand, actually cause a disruption in normal functioning and/or such an intense reaction that it becomes a problem to the individual.
Specific phobias are typically treated with some version of exposure therapy (a gradual process of tolerating of the source of the anxiety). This is usually bolstered by cognitive behavioral therapy or supportive therapy. EMDR is another technique that has had good results, along with hypnotherapy, relaxation techniques, and biofeedback.