“The modern calendar contains 365 days, the actual time it takes for Earth to orbit its star is slightly longer—roughly 365.2421 days. Over decades and centuries that missing quarter of a day per year can add up.”
Missing quarter of a day? Missing? It’s an EXTRA quarter of a day. History.com didn’t learn their math.
Its poorly worded. It's not missing, it is simply not accounted for on a calendar.