A hot key is a key combination that generates a WM_HOTKEY message. The message is routed to a particular window, regardless of whether or not that window is the current foreground window or focus window.
You define a hot key by calling the RegisterHotKey function and specifying the combination of keys that generates the WM_HOTKEY message, the handle of the window to receive the message, and the hot key identifier. When the user presses the hot key, the system places a WM_HOTKEY message in the message queue of the thread that created the specified window. The wParam parameter of the message contains the hot key identifier. Before the application terminates, it should use the UnregisterHotKey function to destroy the hot key.