It’s a leap yer this yer, 2020. That means February gets an extra day. As it says in the rhyme “30 days hath September, April, June and November. All the rest have 31, except February alone which has 28, but 29 each leap year…”.
So why the extra day? Because the year is actually about 365.25 days. So if you didn’t add the extra day on every four years the year would drift and that would throw the calendar out. So in a few years new years day, for instance would be earlier and earlier.
It’s for the same reasons that we have lea seconds added every few years, that makes our time more accurate. The fact that our year isn’t exact effects things like GPS, so it has to be adjusted. When we had old fashioned clocks it wasn’t so important, but even a few centuries ago it was recognised that the year had drifted and the calendar was changed. People actually complained about it. I don’t remember exactly, but I think they had lost a few days of their lives.
I feel sorry for people born on the 29th of February, they only get to celebrate their birthday every four years.