This year is a leap year, meaning there are 29 days in February instead of the usual 28.
I actually have a cousin who was born on February 29, so we jokingly “celebrate” his birthday only every four years. The whole idea was invented by Julius Caesar to align the Roman calendar with the seasons, which it most certainly was not at that time. It had gotten totally out of whack, with harvest festivals showing up in Spring and whole months at a time just left off the calendar. Caesar added months, deleted others, invented Leap Year, and anchored the calendar to the seasons.
This gave us the longest year in recorded history: 46BC, also known as The Year of Confusion.
Part of the problem was that Roman emperors felt they could just add months to the year whenever they thought things needed aligning. There was a whole month (Mercedonius) that could just be tossed into a year whenever desired. As a result, nothing actually aligned with anything meaningful. Caesar’s answer was to give 46BC 15 months and line it up with the seasons, after which it could be restored to the original 12-month year–with the new addition of the Leap Year to keep things aligned with the seasons.
If you’d like to know the whole, totally confusing story of the Gregorian Calendar, you can find several good websites on the topic. I don’t have the time to detail everything today. I’m just concerned with tomorrow, the 29th of February, 2024.