VDT (video display terminal, or sometimes visual display terminal) is a term used, especially in ergonomic studies, for the computer display . A display is a computer output surface and projecting mechanism that shows text and often graphic images to the computer user, using a cathode ray tube ( CRT ), liquid crystal display ( LCD ), light-emitting diode, gas plasma, or other image projection technology. The display is usually considered to include the screen or projection surface and the device that produces the information on the screen. In some computers, the display is packaged in a separate unit called a monitor .
Major issues related to the VDT include the readability of content relative to other media such as paper; the effect of prolonged visual interaction with display content in terms of eye and other muscular fatigue and deterioration; proper viewing distances; and the amount and effect of exposure on users to the extremely low-frequency ( ELF ) radiation that emanates from VDTs.