A day is a 24-hour period, or the length of time it takes the Earth to rotate fully on its axis. There are 365 days in a year, and 31 days in the month of January. DAY definition: 1. a period of 24 hours, especially from twelve o'clock one night to twelve o'clock the next night…. Learn more. The time taken for the Earth to make a full rotation about its axis with respect to the fixed stars; a sidereal day or stellar day. (informal or meteorology) A 24-hour period beginning at 6am or sunrise. A day is a 24-hour period, or the length of time it takes the Earth to rotate fully on its axis. There are 365 days in a year, and 31 days in the month of January. The meaning of DAY is the time of light between one night and the next. How to use day in a sentence. Cambodia Independence Day marks November 9, 1953, when King Norodom Sihanouk negotiated full independence from France — ending nearly a century of French colonial rule that had reduced the Khmer Empire’s civilization to a protectorate administered from Saigon. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cycle drives circadian rhythms in many organisms, which are vital to many life processes. It is daytime on the side of the Earth that is facing the Sun. When it is nighttime, that side of the Earth is facing away from the Sun. It takes 24 hours for the Earth to spin once, so that is one day, including the daytime and nighttime. This is mean solar time, measured relative to the Sun. Details about today's date with count of days, weeks, and months, Sun and Moon cycles, Zodiac signs and holidays. 1. Of or relating to the day. 2. Working during the day: the day nurse. 3. Occurring before nightfall: a day hike.