What is an astronomical unit?​

Astronomical unit (AU, or au), a unit of length effectively equal to the average, or mean, distance between Earth and the Sun, defined as 149,597,870.7 km (92,955,807.3 miles).

Explanation:

The astronomical unit is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres or ~8 light minutes. The actual distance varies by about 3% as Earth orbits the Sun, from a maximum to a minimum and back again once each year.

Explanation:

It is defined as the distance from the center of the earth to the center of the sun. Numerically that's  149.6 million kilometers