When the editor is called up an editor window is created and displayed (for those already familiar with Emacs running on a tty terminal, note that in this context a window is an object used by the window manager to display data, and not a term used to describe a portion of the editor display). The largest area of the editor window is taken up by an editor pane. Each window contains a single pane and therefore the term window is used throughout this manual as being synonymous with pane , unless more clarification is required.
Initially only one editor window is displayed. The corresponding editor pane is either blank (ready for text to be entered) or contains text from a file to be edited. The editor window displays text using the font associated with the editor pane.
It is not technically correct to say that a window displays the contents of a file , rather that each window displays the contents of a buffer . A buffer is an object that contains data from the point of view of the editor, whereas a file contains data from the point of view of the operating system. A buffer is a temporary storage area used by the editor to hold the contents of a file while the process of editing is taking place. When editing has finished the contents of the buffer can then be written to the appropriate file. When the user exits from the editor, no information concerning buffers or windows is saved.
In most cases, there is one buffer for each file that is accessed, but sometimes there is more than one buffer for a single file. There are also some buffers (such as the Echo Area, which is used to communicate with the user) that are not necessarily associated with any file.
LispWorks Editor User Guide (Unix version) - 17 Aug 2017