How to distinguish between a normal year and a leap year?

How to judge a normal year and a leap year: either a leap year or a normal year?

Judgment method of leap year: leap year is divided into ordinary leap year and century leap year. An ordinary leap year is a year divisible by 4 but not by 100. A century leap year is a century leap year divisible by 400.

Average year: refers to the year when there is no leap day in the solar calendar or no leap month in the lunar calendar.

Leap year: leap year is a term in the Gregorian calendar. Where there is a leap day (February 29th) in the solar calendar, the rest of the year is a leap day. Time difference between lunar calendar and tropic year. 1996 and 2 104 are leap years, but 2 100 is a normal year. So it is wrong to say "once every four years". The correct statement should be: "every four years, it will not leap for a hundred years, and it will leap again for four hundred years."