A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. Monitors generally conform to one or more display standards. Sometimes the name "display" is preferred to the word "monitor", as the latter is perceived to be ambiguous alongside the other senses of "monitor" meaning "machine-level debugger" or "thread synchronization mechanism". Computer displays are sometimes called heads, especially when talking about how many are connected to a computer. Computer displays have also been known as visual display units or VDUs.