Once every 4 Years, today occurs. Last year, today would have been March 1... but this year today is tomorrow.
The Earth orbits the moon every 365.25 days (actually: 365 days, 5 hours, 49 minutes, and 16 seconds). So, in order to create a truly annual calendar, an adjustment was required.
But Why February 29?
As part of Julian reform, the day following the Terminalia (February 23) was doubled, forming the "bis sextum"—literally 'double sixth."
Since February 24 was 'the sixth day before the Kalends of March' using Roman inclusive counting (March 1 was the 'first day'). Although exceptions exist, the first day of the bis sextum (February 24) was usually regarded as the intercalated or "bissextile" day since the third century.
February 29 came to be regarded as the leap day when the Roman system of numbering days was replaced by sequential numbering in the late Middle Ages.
If you followed that garble, good. if not, it basically says "Romans had some weird social laws that carried over to more modern times."
Enjoy Leap Day Everyone!!! Real Life is For March!