Yeah, it’s a thing. It’s not a holiday. It’s not a celebration. It’s a mathematical fudging to keep the year kind of synchronized with the Seasons.
AFAIK, it’s the only calendar (the Gregorian/Julian) that observes the leap day anywhere other than the last day of the year.
IF February 29th were the last day of the year, then a few things would fall into place. March 1st would be the New Year. September, October, November, December, which literally mean 7th, 8th, 9th, 10th months, yet we number 9, 10, 11, 12, will actually align with their names.
It also makes it clear that the Gregorian Calendar is dedicated, at its foundation, to the Roman God of War, hence, it begins with March 1st, the month of Mars. January, named after Janus, is the two-faced god. I’ll leave you to draw your own conclusions.
also, the period of the leap day, 1 every 4 years, with exceptions 3 years out of every 400, isn’t as accurate as alternative schedules. 1 exception every 128 years is closer to the Tropical Year, and the Persian schedule is smoother.
There are an awful lot of time frames to choose from, so why do we choose this one which is so awful?
Rethinking Time 