Personal development (also known as self-development or personal growth) comprises the development of the self.
The term may refer to traditional concepts of education or training, but it is also associated with the New Age movement through professional development business trainers who offer counselling and coaching of personal transformation and "inner pathways" to solve social and psychological issues.
To understand this further: a man can have different personalities (at home / at office / at parties etc) but his personal self is one and cannot differ on each ocassion. When someone is referring to personal development then he is meaning a full and total transformation from deep within and not just a temporary personality change for the occasion alone.
See also