Gregorian calendarGre·go·ri·an calendar
a corrected form of the Julian calendar, introduced by Pope Gregory XIII in 1582 and now used in most countries of the world: it provides for an ordinary year of 365 days and a leap year of 366 days every fourth, even year, exclusive of the final year of a century, which is a leap year only if exactly divisible by 400
The solar calendar used in most of the world, sponsored by Pope Gregory XIII in 1582 as a corrected version of the Julian calendar. See Table at calendar.
Named after Pope Gregory XIII who decreed it should be used.