For all intents, a window only exists while it is displayed on the terminal. Once removed from the display, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached. When you use Emacs on an ordinary display terminal, Emacs subdivides the terminal screen into Emacs windows.
Most window systems support arbitrarily located overlapping windows.
Because of the way in which Emacs creates new windows and resizes them, you can't create every conceivable tiling on an Emacs screen. See section Splitting Windows . Also, see section The Size of a Window . See section Emacs Display , for information on how the contents of the window's buffer are displayed in the window. This function returns t if object is a window.