Social anxiety disorder also called social phobia, is a kind of anxiety disorder in which a person has an excessive fear of social situations. It is one of the most common anxiety disorders, and is much more than just "shyness". A person suffering from social phobia, has this constant fear that he is being closely watched and judged by others, and that he will make mistakes, which will lead to criticism from others. As a result of this fear, the person either is in extreme distress in certain social situations or ends up avoiding them.
Most people with social anxiety disorder suffer "anticipatory" anxiety i.e. the fear of a situation much before it even happens. They would get nervous thinking about it for days or even weeks before the actual event. In a few cases, the person is even aware that his/hear fear is unreasonable but is unable to overcome it.