Question: Why is there a leap year every four years? Why is it always in february?

Dalya Soond answered on 15 Jun 2011:

Leap years are there to keep the calendar in sync with the seasons. ACtually, it’s probably not necessary to do, but people like to have their festivals decided by the date to come out at a certain time. For instance, it would be silly to have harvest festivals which are very common throughout the world come out in the middle of winter.

The reason they aren’t normally in sync is because a normal year is not actually 365 days, it’s 365 days and 6 hours.
To correct for this, in the Gregorian calendar, we get an extra day every 4 yrs (because 4 yrs X 6hrs is 24 hrs or one extra day). Leap Day was added on in February because in Roman times when the calendar was calculated, February was the last month of the year, not December.

There are other types of leap years as well. For instance, the Hebrew calendar gets an extra month 7 times over 19 years to keep their calendar (with shorter months) up to date with seasons while the Muslim calendar has no leap years and so months do not reflect seasons.