Windows Aero is a visual desktop experience introduced in Windows Vista and also present in Windows 7. It provides graphic effects, appealing color and translucent windows. Windows Aero is available in the Home Premium, Ultimate, Business and Enterprise editions of Windows. Aero (which stands for "authentic, energetic, reflective and open") brought in new changes to the look and feel of window elements, appearance, layout and functionalities. In Windows 8 and later versions, however, the Aero glass theme and transparency effects were replaced by the Metro design.
Techopedia explains Windows Aero
Windows Aero is usually enabled by default by the operating system, but can disabled as desired. It has specific system requirements depending on the Windows version. Pre-installed themes are available for users to customize. If Aero is not enabled, users may right click on the desktop and select Personalization and then Window Color and Appearance. Certain applications in Windows Vista need Windows Aero to function, such as Flip 3D and Windows Flip. Aero features were enhanced in later versions of Windows. Aero Peek, Aero Snap and Aero Shake were introduced in Windows 7. Windows 8, however, introduced the Metro style, which replaced many Aero features.
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.