The point, in any trajectory of an object in space, where it is farthest from the Earth.
The highest point.
The point, in an orbit about the Earth, that is farthest from the Earth: the apoapsis of an Earth orbiter.
The point, in an orbit about any planet, that is farthest from the planet: the apoapsis of any satellite.
A gap permitting passage through.
The first few measures of a musical composition.
The first performance of a show or play by a particular troupe.
The initial period when a show at an art gallery or museum is first opened, especially the first evening.
A vacant position, especially in an array.
An unoccupied employment position.
In mathematical morphology, the dilation of the erosion of a set.
An act or instance of making or becoming open.
A time available in a schedule.
An opportunity, as in a competitive activity.
An act or instance of beginning.
The first few moves in a game.
Pertaining to the start or beginning of a series of events.
describing the first period of play, usually up to the fall of the first wicket; describing a batsman who opens the innings or a bowler who opens the attack