Definition
Ad hoc widgets: non-standard widgets developed specifically for a GUI (graphical user interface). Such widgets involve multi-event interactions (in opposition to mono-event interactions, e.g. multi-touch interactions for zooming, rotating), and/or multi-modal interactions that aim at being more adapted, natural to users.
A simple example of such widgets is the drawing area of graphical editors with which users interact using more complex interactions such as pencil-based or multi-touch interactions.
GUIs containing such widgets are called Post-WIMP GUIs