On macOS, a GUI app that was running in fullscreen appears to still be open after being quit or force-quit: Mission Control keeps showing a tile for it in the Spaces bar at the top, often rendered as a solid black thumbnail with the app's name under it. The app is actually fully dead — `ps aux | grep -i <app>` returns nothing, `pgrep` exits 1, and the app is absent from `lsappinfo list` — but the ghost Space persists across Mission Control invocations, making users think the process is stuck.