A window manager is the software that controls the layout and operation of the windows on the screen. Blackbox is a window manager.
The window manager is just another X client (see XWindowSystem), but it can do a lot to make the entire graphical user interface easy to use, such as:
- Rendering a frame around windows and titlebars on top of windows.
- Providing window menus and buttons for various window operations.
- Overlapping and resizing windows.
- Auto-arranging windows.
- Controlling where you can type (which window has focus).