Is 2 100 a leap year? Why?

According to the definition of leap year, leap every four years, but not every hundred years, but every 400 years. So 2 100 is a multiple of 4, but it is a century year, not a leap year.

Leap year is a kind of western calendar, which was introduced to julian calendar in 45 BC. It was set up to solve the error between Gregorian calendar and solar calendar. In leap years, February has 29 days instead of 28. In addition to the Gregorian calendar, the China lunar calendar can be divided into "Runnian" and "Pingnian". In the traditional customs of China, Runnian has special significance, such as various celebrations and festivals.