The Gregorian calendar is the calendar system most widely used today. Introduced by Pope Gregory XIII in 1582, it was designed to correct inaccuracies in the previous Julian calendar, which miscalculated the length of the solar year. The Gregorian calendar consists of 12 months, totaling 365 days in a common year and 366 days in a leap year. This calendar divides the year into months of varying lengths: January has 31 days, February has 28 or 29 days, and so on. The Gregorian calendar is essential for organizing time, scheduling events, and coordinating activities across the globe.