1) Government by three 
[theory] The theory of triarchy (from the Greek τρι- `three` and ἄρχω arkho, `to rule`) refers to the (supposed) three fundamental ways of getting things done in organizations: hierarchy, heterarchy and responsible autonomy. All organizations use a mixture of these three ways, but the proportions can differ widely. At present, hiera...
government by three people
• (n.) Government by three persons; a triumvirate; also, a country under three rulers.
triarchy 1. The government or jurisdiction of a triarch; one of three divisions of a country ruled by triarchs. 2. Government by three rulers or powers jointly; three persons associated in government, a triumvirate. 3. A group of three districts or divisions of a country each under its own ruler.