Definitions for "Active window"
interface: The frontmost window on the desktop; the window where the next action will take place. An active window's title bar is highlighted.
the window that appears in front of any other windows on the screen. Any keyboard entry into the computer will be processed first by this window.
The window in which a user is currently working or directing input. An active window is typically at the top of the Z order and is distinguished by the color of its title bar. Compare inactive window.