A screenshot, screen capture (or screen-cap), screen dump, screengrab is an image taken by the computer user to record the visible items displayed on the monitor, television, or another visual output device. Usually, this is a digital image using the operating system or software running on the computer, but it can also be a capture made by a camera or a device intercepting the video output of the display.
In the 1980s, computer operating systems did not universally have built-in functionality for capturing screenshots. Sometimes text-only screens could be dumped to a text file, but the result would only capture the content of the screen, not the appearance, nor were graphics screens preservable this way. Some systems had a BSAVE command that could be used to capture the area of memory where screen data was stored, but this required access to a BASIC prompt. Systems with composite video output could be connected to a VCR, and entire screencasts preserved this way.
Screenshots can be used to demonstrate a program, a particular problem a user might be having, or generally when display output needs to be shown to others or archived. For example, after being emailed a screenshot, a Web page author might be surprised to see how their page looks on a different Web browser and can take corrective action. Likewise with differing email software programs, (particularly such as in a cell phone, tablet, etc.,) a sender might have no idea how their email looks to others until they see a screenshot from another computer and can (hopefully) tweak their settings appropriately.