[Someone]

https://en.wikipedia.org/wiki/Astronomical_unit:

”Originally conceived as the average of Earth's aphelion and perihelion”

https://www.britannica.com/science/astronomical-unit:

”a unit of length effectively equal to the average, or mean, distance between Earth and the Sun”

I wondered whether the two are equal. A bit to my surprise, they are (http://www.farmingdale.edu/faculty/sheldon-gordon/RecentArti...)

(If we take into account that earth moves faster near its perihelion, I think that will break down)

And, nitpick, nowadays, the AU apparently is exactly 149,597,870,700 meters.