A leader is someone who people naturally follow through their own choice, whereas a manager must be obeyed. A manager may only have obtained his position of authority through time and loyalty given to the company, not as a result of his leadership qualities. A leader may have no organisational skills, but his vision unites people behind him.
Management usually consists of people who are experienced in their field, and who have worked their way up the company. A manager knows how each layer of the system works and may also possess a good technical knowledge. A leader can be a new arrival to a company who has bold, fresh, new ideas but might not have experience or wisdom.