La rotación y revolución de la tierra: la tierra girando

The video explains how the Earth rotates on its axis and revolves around the Sun at a speed of 109,000 km/h. It takes 365.25 days for a complete revolution, leading to the addition of an extra day every four years, known as a leap year, resulting in 366 days instead of the usual 365.

Why is there an extra day added every four years?

What is a leap year and how often does it occur?