Menus are text structures that respond to mouse clicks (and usually certain Alt-key sequences) to enable users to give commands to the program. There are three types of menus in Windows. 1) Ordinary window menus that start just below a window's caption and drop down to reveal sub options when they are clicked (see %mn). 2) The so called system menu, that can be activated by clicking in the top left corner of a window (see %sm), and 3) popup menus that appear when the right mouse button is clicked (see %pm). See also shortcut keys.