day

Time taken for the Earth to rotate once on its axis. That part of the Earth's surface at any one time facing the Sun experiences day. As the Earth rotates, these parts move to face away from the Sun, receiving no direct sunlight, and experience night.

The solar day is the time that the Earth takes to rotate once relative to the Sun. It is divided into 24 hours, and is the basis of our civil day. The sidereal day is the time that the Earth takes to rotate once relative to the stars. It is 3 minutes 56 seconds shorter than the solar day, because the Sun's position against the background of stars as seen from Earth changes as the Earth orbits it.