The solar year is 365 days 5 hours 48 minutes 46 seconds which is the time between two successive occurrences of the vernal equinox. As a decimal, that would be about 365.2422 days per year.
Now our calendar is based on whole days (1 complete rotation of Earth on its axis back to the same position relative to the sun) so it is treated as 365 days each year.
To account for the slightly extra length of an actual year, we add a leap year generally every 4 years. A leap year has 366 days so that would make it up to 365.25 days per year. However, as you can see, that's still not exactly 365.2422, so we have one additional rule. If the year is divisible by 100 (1900, 2000, 2100, 2200, etc.) it is NOT a leap year, *unless* it is divisible by 400 (2000, 2400, 2800, etc.). That rule takes out 3 days every 400 years and that brings us to 365.2425 days per year on the calendar.
There is still an inaccuracy in our calendar that will mean that we will need to eventually drop a leap day somewhere down the line, but that won't be for something like 3,000 years, so it's not worth worrying about right now. By then, the rotation of the earth might be longer requiring a different adjustment to the calendar.
At present a mean solar year is 365 days 5 hours 48 minutes 46 seconds. On our current calendar, we account for that with most years having 365 whole days, but then adding 97 leap days spread over 400 years.
P.S. Were you being serious when you asked this? At least if you are going to troll the Mathematics category, you could take the time to pick a best answer. :)