A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. The calendar can also be used for tracking events, appointments, birthdays, and other important dates.
The Gregorian calendar is the most widely used calendar in the world today. It was introduced in 1582 by Pope Gregory XIII as a modification of the Julian calendar, which had been in use since 46 BC. The Gregorian calendar is a solar calendar, meaning that it is based on the Earth’s orbit around the sun.