Activation / Deactivation
A window is called active when it has the keyboard input focus (or simply the focus), i.e. it exclusively receives all the notifications about the keys being pressed; all the other windows are called inactive. Active window is visually marked by its bright title bar while inactive windows have their title bars dimmed. Like the current player in a game of billiards whose turn it is to shoot while all the others stand idly by and wait their turn, only one window at a time can have the focus - so when you switch from one window to another the first one becomes inactive and the second one is activated. The active window is marked by highlighting its title bar while the others have their title bars dimmed.
Therefore, the Deactivation trigger allows automatic performance of actions when a window loses the focus (i.e., becomes the inactive window). Conversely, the Activation trigger allows automatic performance of actions when a window gets the focus. In most cases, Activation trigger performs the actions that are opposite to those triggered by the Deactivation trigger or simply restores the previous values of window properties changed by the Deactivation trigger. The following actions can be triggered upon deactivation: