"Aero" is the name of the transparent, glass-like UI present in Windows Vista and Windows 7. It originated with Longhorn's Aero Glass, first seen in Longhorn 4039.
Aero in Windows Vista and 7 requires a capable GPU to render the transparency. In Windows 8 M2 and up, Aero is rendered in software, allowing one to have Aero on any video card, but taking a toll in overall system performance.
The new aero theme in Windows 8 made it's debut when it was unlocked in build 7989, changing the Aero appearence drastically for the first time in 6 years since the Vista beta era.
