All leaders hold a position of authority and may utilize the power that comes from their position

Formal Leaders (Eg : C.E.O)

Explanation:

Leadership is act of guiding, motivating people towards achievement of a common goal.

The leaders who hold a position of authority and may utilize the power that comes from their position to influence others' actions : are Formal Leaders. These leaders exercise 'formal leadership' where the person is officially designated as group leader. The leader exercises power given to him/her as per the position he/ she has in the organisation.  

Example of Formal Leader : Chief Executive Officer (C.E.0)

However there are another type of : natural informal leaders  also, who just demonstrate personal influential leadership skills, without formal official designation.