A polar orbit has an inclination of (or very close to) 90 Degrees against the Equator. A satellite on a polar orbit therefore passes above both poles of the planet on each revolution.

Since the satellite has a fixed orbital plane perpendicular to the planet's rotation, it will pass over a region with a different longitude on each of its orbits, therefore flying over every point on the planet twice within one day.

Polar orbits are often used for earth-mapping-, earth observation- and spy satellites, as well as some weather satellites.