From the "did you know" department: Aero is (sort of) AERO because it actually stands for "Authentic, Energetic, Reflective and Open".
These are words that can be interpreted however you like. Does authentic mean "not fake" or does it mean "true to the thoughts the user has about how to interact with the OS?" How can a UI be energetic? Does that just mean lots of bright colours, glowing jelly buttons, and animations? What does the UI reflect? And open to what?
I will say this though, they are all positive and pleasant words, and if a team held those words up as goals while working on software for me, I would expect that they would make me pleasant software. In a UI, that's a good thing.