- "Greenscreen" is a video and film compositing technique, better known as bluescreen.
Green screen was the common name for a monochrome CRT computer display using a green phosphor based coating. They succeeded teletype terminals and preceded colour CRTs as the predominant visual output device for computers. They were abundant in the early-to-mid-1980s, together with amber screens.
The most famous green screen product is arguably the original IBM PC monochrome display, designated the IBM 5151 (the PC itself had the model number 5150). From the outset, the 5151 was designed to work with the PC's Monochrome Display Adapter (MDA) text-only graphics card, but soon the third-party Hercules Graphics Card became a popular companion to the 5151 screen because of the 'Herc's high-resolution bitmapped monochrome graphics capability, much used for business presentation graphics generated from e.g. spreadsheets like Lotus 1-2-3.
Some green screen displays were furnished with a particularly full/intense phosphor coating, making the characters very clear and sharply defined (thus easy to read), but generating a somewhat disturbing afterglow-effect (sometimes called a "ghost image") when the text scrolled down the screen or when a screenful of information was quickly replaced with another as in word processing page up/down operations. The 5150 belonged to this category. Other green screens avoided the heavy afterglow-effects, but at the cost of much more pixelated character images.
The ghosting effects of now-obsolete green screens have become an eye-catching visual shorthand for computer-generated text, frequently (and ironically) in "futuristic" settings.. The Ghost in the Shell and Matrix series science-fiction films prominently feature computer displays with ghosting green text. The XScreenSaver package of screen savers by Jamie Zawinski also includes a screen saver called Phosphor that prints green text with a simulated ghosting effect.