1A newly established frontier, especially (in U.S. History) one marking a westward expansion of pioneer settlement. Later also: a region offering new opportunity, especially one which is unfamiliar.
2In extended use. Generally. Anything which marks or indicates the limits of the present state of knowledge, policy, etc., especially as a starting point for new work; a new challenge; a new development.
historical In form New Frontier. A programme of social improvement advocated by John F. Kennedy, President from 1961 to 1963.
Mid 19th century; earliest use found in The North American Review. From new + frontier.