A day is a unit of time. In common usage, it is an interval equal to 24 hours. It also can mean the consecutive period of time during which the Sun is above the horizon, also known as daytime. The period of time during which the Earth completes one rotation with respect to the Sun is called a solar day.

A day is a unit of temporal measurement for a literal day or epoch of time. Day, DAY or Days may also refer to:

• Daytime (astronomy)
• Awareness day, a date set by a major organisation or government to commemorate a cause of importance on a national or international level