Used to describe participants in international relations e.g, States, Non Governmental Organizations and Multi National Corporations.
1. A theatrical performer.
2. One who takes part; a participant: "France, Britain . . . and any other external actors now involved . . . in the affairs of the continent" (Helen Kitchen).
3. Law One, such as the manager of a business, who acts for another.
4. A participant that contributes to something.
http://www.thefreedictionary.com/actors