An output device is any hardware that allows the communication, in the form of graphs, pictures, sound ... of the result of a computer activities to the outside world. Typical examples are monitors, lcd screens, printers, plotters, speakers and speech synthesisers.
Speakers attached to a computer in exactly the same way as speakers are attached to a stereo system. As the use of computers becomes more widespread, more are being sold as multimedia systems, i.e. they have the capability to act as stereo, audio-visual recording and playback systems.
Speakers may be self powered with their own small amplifier built in and they usually require a soundcard to be fitted inside the computer, to which the speakers are then connected.
Speech synthesizer software is able to translate written text from a file into audible speech. This has specialised uses, particularly relevant to those individuals with impaired vision, speech or manual dexterity.
Printers are used to produce paper copies of any text, numerical or graphics material processed by the computer. A Plotter is a more specialised type of printer that uses computer software to control a pen, moving in two dimensions over the paper. They are ideally suited to produce larger, more complex prints, e.g. technical drawings, engineering or architectural plans and maps.
Touchscreens are screens that not only display information, but can react to touch. These and certain other devices such as modems, can be classed as Input/Output devices.
A Plotter is an output device used in engineering to draw graphs on paper.