The term "stakeholder" has already been used without giving a definition:
Stakeholder: An individual, group of people, organisation or other entity that has a direct or indirect interest (or stake) in a system.
A stakeholder's interest in a system may arise from using the system, benefiting from the system (in terms of revenue or other advantage), being disadvantaged by the system (in terms, for instance, of cost or potential harm), being responsible for the system, or otherwise being affected by it. Stakeholders are legitimate sources of requirements.