Window or user interface chrome, which incidentally is where Google Chrome gets its name (as the “chrome” for the web) which is probably infesting your results. Going to Wikipedia’s “Chrome” disambiguation would get you a one-line description too but the page-link would just direct you to graphical user interfaces.
Chrome is all the stuff that’s not the content area in a GUI. So the user-agent you’re reading this in has a content area loading the page this thread is on (most likely a web browser but maybe you’re using an HN-specific app), and then a toolbar where the location bar lives, maybe a favorites bar and the window controls like close and minimize unless you’re on a phone. Basically chrome is all the overhead GUI like menus, toolbars, sidebars, pop-overs and controls around the stuff you’re focused in on.
Chrome is all the stuff that’s not the content area in a GUI. So the user-agent you’re reading this in has a content area loading the page this thread is on (most likely a web browser but maybe you’re using an HN-specific app), and then a toolbar where the location bar lives, maybe a favorites bar and the window controls like close and minimize unless you’re on a phone. Basically chrome is all the overhead GUI like menus, toolbars, sidebars, pop-overs and controls around the stuff you’re focused in on.