A term in event-driven programming ; a function that processes an event; often a synonym for callback.
See also signal handler.
hints
(window manager) X Window System applications can ask for special treatment from the window manager. Examples of hints include specification of where windows should appear on the display, that the window should not be obscured, and the layer order. Earlier, GNOME and KDE used a set of incompatible hints, but they now use a unified hint system called NET_WM Hints [XDG].