Final answer:
An AU is an Astronomical Unit, the average Earth-Sun distance used in celestial measurements. In thermodynamics, AU also represents a stored quantity of energy. Politically, AU refers to the African Union, promoting stability in African nations.
Step-by-step explanation:
An Astronomical Unit, commonly abbreviated as AU, is a unit of distance equal to the average Earth-Sun distance, which is approximately 149.6 million kilometers (1.496 × 10¹¹ m). The reason the AU is defined as the average distance rather than the exact distance is that the Earth's orbit around the Sun is not a perfect circle, but an ellipse; therefore, the distance varies throughout the year.
In terms of energy, both Q and W represent energy in transit, while AU represents an independent quantity of energy that can be stored. This distinction is important in thermodynamics, where the change in energy of a system is equal in magnitude but opposite in sign to the change in energy of its surroundings.
Politically, the AU refers to the African Union, working to foster political stability in countries experiencing turmoil, such as Sudan. The African Union's peacekeeping troops aid in this effort and also attempt to resolve legal issues regarding border and territorial disputes.