Wikipedia
In graphical user interfaces, the window decoration is a part of a window in most windowing systems.
A windows decoration typically consists of a title bar, usually along the top of each window and a minimal border around the other three sides. On Microsoft Windows this is called "nonclient area".
In the predominant layout for modern window decorations, the top bar contains the title of that window and buttons which perform windowing-related actions such as:
- close
- maximize
- minimize
- resize
- roll-up
The border exists primarily to allow the user to resize the window, but also to create a visual separation between the window's contents and the rest of the desktop environment.
Window decorations are considered important for the design of the look and feel of an operating system and some systems allow for customization of the colors, styles and animation effects used.