| Word | Description |
| D.D. (Direct Drive) | An Auto Iris lens requiring a D.C. reference from the camera rather than the traditional video reference. |
| Daisychain | To connect devices in a series, one after the other where the transmitted signals go to the first device, then to the second and so on. |
| Data cable | Cable used for transmitting low level signals between system units. |
| dB | Decibel, a logarithmic unit for comparing two voltages, each 6dB doubles the voltage. |
| DC | Direct Current |
| Default | An assumption made by the system when no specific choice is given by the programme or the user. |
| Depth of Field | The area of acceptable focus of an image. The wider you set the aperture of a lens the lower the depth of field becomes. |
| Digital | A signal that levels are represented by binary numbers. These can be kept in a store. |
| Distribution Amplifier | A device that accepts a video signal and sends it out over a number of independent outputs. |
| DOS | A disk operating system in which programmes are stored on disk. |
| Duplex | A multiplexer with two frame stores allowing it to show multi-screen pictures while performing time multiplex recording. |
| DVD (Digital Video Disk, Digital Versatile Disk) | A de facto standard agreed on by the computer, consumer electronics and entertainment industries for storing 4.7 or more GB of data on a single optical disc the size of a CD. |
| DVR | Abbreviation of Digital Video Recorder, a device that uses digital techniques to record CCTV pictures. The results can be of higher quality than VHS or SVHS. Events can be found faster and there is no loss of quality when copies are made. |
| Dwell Time | The length of time a switcher will hold a camera before moving on to the next in sequence. |