Century leap year
In the Gregorian calendar, a century leap year is a year that is exactly divisible by 400 (and qualifies for the adding of February 29, like all other leap years). For example, the years 1600 and 2000 were century leap years; the century years 1700, 1800, and 1900 were not century leap years. The next century leap year will occur in the year 2400. Century leap years always begin on a Saturday, and February 29 always falls on a Tuesday.
The Gregorian calendar more accurately tracks Earth's revolution around the Sun, more so than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. Because of this, the Julian calendar began to gradually drift with respect to the four seasons. Each season has been occurring earlier and earlier over time. Therefore when the Gregorian calendar was created in 1582, it eliminated this problem by specifying that end-of-century years are only leap years if divisible by 400.