Gregorian calendar, also known as the solar calendar, was mentioned earlier. The dates on the calendar in Arabic numerals are Gregorian calendar dates. For example: October 10, 2000, is a Gregorian calendar date.

The Gregorian calendar is the world's common calendar system.

The Gregorian calendar has 365 days or 366 days in a year. A year with 366 days is a leap year, and every four years is a leap year, while the rest are common years. A year divisible by 4 is a leap year. For example: 2000, 2004, 2008, 2012, etc., are all leap years.