A menu which appears in response to a user action (typically a mouse click) and whose contents are determined by which application window was clicked or has the input focus.
Most GUIs use a secondary mouse button (right or middle) to call up a context-sensitive menu as the primary mouse button is normally used to interact with objects which are already visible.
The context-sensitive menu often contains functions that are also available in a menu bar but the context-sensitive menu provides quick access to a subset of functions that are particularly relevant to the window area clicked on.
The RISC OS WIMP uses only context-sensitive menus (always invoked using the middle mouse button). This saves screen space and reduces mouse movement compared to a menu bar.