With the exception of some paginators, windows can be moved and resized without affecting the execution of their clients. Overlapping windows do not affect each other. One special window is the root window, which forms the background of the display. Inside the root window you can perform window management functions rather than ordinary input and output with a window. Windows can also be represented by icons.
Icons are small rectangular symbols used to keep many clients from cluttering the screen.
Generally, you cannot send input to a client's icon. After completing input, you can iconify the window to convert it into an icon. A client will continue to execute when in its iconic form. For example, you can open a window, enter the input to run a program, and iconify the window. At some later time you can de-iconify the icon to view the program's output.