Google published a Google Doodle about „why is there a leap day?“ on Februaray 29th 2016. On the Google homepage worldwide there was published the Leap Year 2016 Google Doodle.
A leap year is a year containing one additional day added to keep the calendar year synchronized with the astronomical or seasonal year.
Each leap year has 366 instead of 365 days. This happen because the astronomical year is not count in days and is a little bit longer than the seasonal year. A leap year take place every 4 years else if the year is divisible by 100 or 400.