The active window

Once you have several windows on the screen, you (and Point) will have to be able to determine which window your commands will affect. At all times, one of the windows is the active window. It is marked by a double-line border and a double line along the top banner. The other windows have a single-line border and use blanks as a fill characters along the top banner. Neither the top window nor the window containing the selection are necessarily the active window.