The point of leap years is to help adjust our Gregorian calendar (aka, the 365-day calendar you can find on your desk or phone) to the solar calendar, and make sure we celebrate solar events like the spring and autumn equinoxes with some regularity every year. Even adding an extra day to February every four years doesn’t quite do the trick, which is why scientists sometimes call for a Leap Second like they did last year on June 30 at 11:59:60 pm.
How do you remember if it’s a leap year? Simple: If the last two digits of the year are divisible by four (e.g. 2016, 2020, 2024…) then it’s a leap year. Century years are the exception to this rule. They must be divisible by 400 to be leap years—so, 2000 and 2400 are leap years, but 2100 will not be one.