Day, symbol d, is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean portion of the full day during which a location is illuminated by the light of the sun, also known as daytime. The period of time measured from local noon to the following local noon is called a solar day.
In 1967, the second was redefined in terms of the wavelength of light, and it became the SI base unit of time. The unit of measurement for time called "day", redefined in 1967 as 86400 SI seconds and symbolized d, is not an SI unit, but it is accepted for use with SI. A civil day is usually also 86400 seconds, plus or minus a possible leap second in Coordinated Universal Time UTC, and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time.List of all Day to other time units individual converters.