The Leap Day, February 29, depicts a day that occurs only once every four years, every Leap Year or intercalary year when an extra day is inserted into the calendar. But not every fourth year; if that year ends in “00,” like 1900, then it is not a Leap Year. Except if that year ending in 00 is also divisible by 400, then it is a Leap Year. Unless it is a Tuesday and it is dark. OK, I made up that last rule.
So, years like 2024 are Leap Years, being divisible by 4. But 1900 is not a Leap Year, as it ends in 00. In the year 2000, you’ll remember the famous Y2K, when computer programmers only obeyed the first two rules and assumed that it wasn’t a Leap Year, so all the computers failed, and the world came to an end. That was a Leap Year, as it was divisible by 4, and though it ended in 00, it was divisible by 400 (indeed, it’s divisible five times, if you’re still with me.)