Tear-off menu
A drop-down menu with a dashed "perforation" at the top: click it and the menu comes loose as a small window of its own that stays on screen.
The idea is that a menu you use constantly ought to be allowed to be a palette. HyperCard let its Tools and Patterns menus be torn off and laid beside the card in 1987, and OPEN LOOK did the same thing the following year with its pushpin: pin the menu and it stays put. Motif 1.2 (1992) adopted the feature under the name tear-off with the resource XmNtearOffModel, and the dashed line became the standard look. Window Maker let every one of its menus be torn off by dragging its title, in NeXT fashion.
It spread furthest through Tk, where every menu was tear-off by default and got a dashed first row. That is why roughly every Python program using tkinter contains the line tearoff=0: generations of programmers have learned what the feature is called solely by turning it off. GTK had GtkTearoffMenuItem until it was deprecated in 2012 and dropped in GTK 4. Torn-off menus always felt a little provisional, and dockable toolbars and panels took over the role in most programs.