Known as a leap year or leap day February 29th is added to most years that are divisible by 4 eg. 2016, 2020 and the next one will be 2024.
This day is added because we have a 365 day year and the earth actually takes a little bit longer than that to orbit the sun. The extra day is added to keep our calendar year on track. It takes 365.2422 days for the earth to orbit the sum.
Leap years were introduced over 200 years ago by the Roman general Julia Caesar. The Julian calendar set the rue the every year that could be divisible by 4 would be a leap year.
Folklore says the reason why February is the shortest month of the year is because Roman emperor Augustus Caesar stole a day from February to add to the month named after him ~ August. However, the real reason February is shorter is because first calendar was only 10 months long. In order to sync the calendar with the lunar year January and February were added.
