Where and when did the [x] first enter into the UI lexicon?

Why do we use an “X” symbol to close or exit? Lauren Archer takes us down memory lane and traces the history of [x] to Close

X’s are everywhere in user interface (UI) design. A powerful symbol, [x] is capable of closing windows and popups, toolbars and tabs and anything else that might otherwise be cluttering up your screen.

Clicking on [x] to close a feature has become an instinctual part of using a computer and a standard in web and software design. Although it may seem like the ubiquitous [x] has always been a part of Graphical User Interfaces (GUI), a quick jaunt through the history of GUIs reveals that this actually isn’t the case.