Any group or individual who can affect or is affected by the achievement of the organisation's objectives.
Anyone who has a responsibility for an expectation or some other interest in the enterprise, e.g. shareholders, users, government, suppliers, customers and the public.
Source: COBIT 5.
person or organization that can affect, be affected by, or perceive themselves to be affected by a decision or activity.
Source: ISO 27000 - Information Security Standards.
Primary stakeholders have a direct impact on the organisation, while secondary stakeholder have an indirect impact. A shareholder is a primary stakeholder, while the government is a secondary stakeholder.
Source:Freeman, R. Edward, 1984, Strategic management: A stakeholder approach.