| Word | Description |
| Hard Disk Drive | Non volatile digital data storage device used in computers. Come in various storage sizes, normally measured in giga-bytes. See Hard Disk Recorder. |
| Hardwired | Method of controlling camera points using multicore cable. |
| HDMI | HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA. |
| HDR | Abbreviation of Hard Disk Recorder, a device that uses digital techniques to record CCTV pictures to a hard disk. 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. |
| Hot Swapping | Removing and replacing a component of a larger system while the system is receiving power and operating. |
| HTML (Hypertext Mark-up Language) | A standard for defining documents with hypertext links. HTML is a subset of SGML (Standard Generalised Mark-up Language) and is used to establish links between documents on the World Wide Web. |
| HTTP (Hypertext Transfer Protocol) | The clients/server protocol used for connections to servers on the World Wide Web. Addresses of Web sites begin with an http://prefix. |
| Hub | A central connecting device in a network that joins communications lines together in a star configuration. |
| Hz (Hertz) | Cycles per second |