Vested interests are people or groups who stand to gain - usually financially - from some policy, often a public policy.
A person can also be said to have a vested interest. For example, a Local Councillor or Member of Parliament may own shares in a company which is being considered for a profitable Public Contract . Elected Representative are usually required to declare all relevant vested interests. Failing to declare any vested interest is seen as corruption.
An Elected Representative is a person who has won a democratic election.