What distance defines the Astronomical Unit (AU) for solar system measurements?

The average distance between the Earth and the Sun.

The Astronomical Unit (AU) is established as the primary intermediate unit for measuring distances throughout our solar system, and its definition is intrinsically linked to Earth's orbital path. Specifically, one AU is fixed as the average distance separating the Earth from the Sun. This value is quantified at approximately $149.6$ million kilometers, or roughly $93$ million miles. This anchoring point provides a consistent and intuitive metric for solar system navigation and comparison, allowing scientists to simplify complex figures—like expressing Jupiter's distance as $5.2$ AU rather than listing its distance in kilometers, which would require dealing with a nine-digit number.