The unit of measure that refers to the average distance between Earth and the Sun is the Astronomical Unit (AU).

Here's a breakdown:

* Definition: One Astronomical Unit (AU) is defined as the average distance between the Earth and the Sun. It's roughly 149.6 million kilometers (93 million miles).

* Why it's important: The AU is a convenient unit for measuring distances within our solar system. It's much simpler to say that Mars is 1.52 AU from the Sun than to use kilometers or miles.

* Not perfectly constant: While the AU is defined as an average distance, the Earth's orbit is slightly elliptical, meaning the distance to the Sun varies throughout the year.

So, the next time you hear about a planet being a certain number of AUs away from the Sun, you'll know it's referring to the average distance from Earth to our star!