Two games played on the same day by the same two teams.
Two race performances in the same day.
Two greyhound racing performances during one day.
Doubleheader is the term used to describe two baseball games played between the same two teams on the same day. (The term originated in the railroad industry; see doubleheader.)
Doubleheader is used by network television to refer to two games in any sport aired back-to-back on the same network, even though they do not involve the same two teams (three such games may be referred to as a tripleheader, this scenario being encountered most frequently in basketball). A doubleheader purposely coincides with a league's scheduling of "early" and "late" games. In North America, games usually start at the same time period in different time zones (Eastern and Pacific).