Any kind of visible output including text, images, movies, line art and digital photographs; stored in bitmap or vector graphic form.
Most modern computers can display non-text data and most use a graphical user interface (GUI) for virtually all interaction with the user. Special hardware, typically some kind of graphics adaptor, is required to allow the computer to display graphics (as opposed to, say, printing text on a teletype) but since GUIs became ubiquitous this has become the default form of visual output. The most demanding applications for computer graphics are those where the computer actually generates moving images in real time, especially in video games.
There are many kinds of software devoted to manipulating graphical data, including image editing (e.g. Photoshop), drawing (e.g. Illustrator), user interface toolkits (e.g. X Window System), CAD, CGI.