Immediate mode GUI
A UI approach where every widget is drawn and handled afresh each frame through direct function calls, with no lasting tree of widget objects.
Instead of creating a button once and subscribing to its events, the code calls if (Button("OK")) … every frame; the return value says whether it was clicked right now. There is no widget to track — all state lives in the application's own variables, and the interface is re-described from scratch as often as the game renders. Casey Muratori popularised the idea and the name in a 2005 talk.
Omar Cornut's Dear ImGui (2014) made the approach ubiquitous in game dev: debug windows, level editors and tweak sliders can be wired up in minutes. The price is that complex, static interfaces get rebuilt needlessly every frame — the opposite, retained mode, keeps a lasting model instead.