Definition - What does Windows Aero mean?
Techopedia explains Windows Aero
One of the key features of Windows Aero is the glass theme for open windows. The behavior of windows was redesigned with subtle animations. Another feature is the taskbar previews of open windows.
Windows Aero provides users with visually appealing effects, appearance and access to applications. Examples of these are the translucent title bars, stylish color schemes and smooth, rounded edges. Windows Aero provides a smoother desktop experience along with dynamic window animations.