Earth orbits the Sun at an average distance of 92.96 million mi (149.60 million km),https://en.wikipedia.org/wiki/Earth’s_orbit. Earth’s orbit is an ellipse with the Earth-Sun barycenter as one focus and a current eccentricity of 0.0167; since this value is close to zero, the center of the orbit is close, relative to the size of the orbit, to the center of the Sun.
One complete orbit takes a little bit more than 365 days. This means that that the Earth revolves around the sun in 365 days, 5 hours, 59 minutes and 16 seconds exactly. The time a planet takes to revolve around the sun is called a year.  https://www.nasa.gov/audience/forstudents/k-4/dictionary/Revolve.html.
Because astronomical events like the Earth orbits the sun do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track. By inserting an additional day into the year, the drift can be corrected. This is the explanation of the leap year which is a calendar year that contains an additional day added to keep the calendar year synchronized with the astronomical year or seasonal year.Meeus, Jean (1998), Astronomical Algorithms, Willmann-Bell, p. 62