The complete legislative and executive control of state or federal government by one party: governorship, the upper house, and the lower house of state or federal legislatures. The party that holds all three positions of power is said to have a trifecta.
The attainment of three important achievements, qualities, etc.
A bet in which the bettor must select the first three placegetters of a race in the order in which they finish.
A set of three related things, often things that cause problems.
An official group of three people, especially a ruling council of three men and particularly (historical) two such councils in Roman history.