Every four years we get an extra day thanks in part to Julius Caesar and Pope Gregory XIII.
The day compensates for the fact that it takes the earth takes 365.2425 days to circle the sun instead of the cut-and-dried 365.
Julius Caesar, with the help of his team of astronomers back in 46 B.C., came up with a calendar that added an extra day every four years. The calendar had the right concept but over time ended up adding too many days.
The modern Gregorian calendar, which was put into use in 1582 under Pope Gregory, gave more specific rules to leap year, saying the extra day could only be inserted on years that are evenly divided by four and not in years ending with an “00″ such as 1900 or 2100 as they aren’t divisible by 400.
Coincidentally, the extra day of leap year, with it’s Februrary placement, does not make Lent 41 days, as this post explains but it could certainly provide some time for extra reflection.