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CCTV Systems - Glossary of Terms [Hardfacts]


An understanding of the terminology used in connection with CCTV systems will enable you to better discuss your requirements with installers. When first talking to a prospective installer, you may encounter these terms:

Operational Requirement (OR)

This is the name of a formal document that attempts to capture details of what it is that any CCTV system is designed to address.  As such it forms the basis for the technical design of any sytem.
BS 8418
This is the UK’s code of practice for detector activated remote monitored CCTV.
NCP 104
This is the code of practice used for non BS 8418 systems by National Security Inspectorate listed companies.
SS 2003
This is the code of practice used for non BS 8418 systems by Security Systems and Alarm Inspection Board listed companies.

Thereafter many other terms will be encountered, with this glossary listing them in the approximate order that they would be encountered within a CCTV system - if starting from the point of image capture and working through to the point(s) where image(s) are viewed/recorded and/or responded to.

Devices to capture images and convert them into an electronic signal for onward transmission. Cameras can be monochrome (black and white) or colour, and in either case may also have an infrared (heat image) capability.
Two types of cameras exist:

  • Tube cameras – Now regarded as old camera technology.
  • Charge Coupled Device (CCD) Camera – Current digital technology.

An optical device to capture and focus light into the camera’s image capture system. Lens types include: zoom, fixed, wide angle or varifocal types.   
Used to position lenses within a camera. Two types are used C and CS mounts.
Shutter controlling the amount of light entering a camera. An iris can be a fixed or auto-iris type i.e. responds to changing light levels automatically.
Name for the pictures captured by CCTV.
The smallest area of the camera CCD that is capable of capturing light falling on it. The greater the number of pixels per defined area the higher the resolution or definition. Pixel capability is usually referred to in terms of ‘megapixels’.  
A description of image quality in terms of the amount of data that can be captured and transmitted. Standard Definition (SD) or High Definition (HD) are the related terms.
Pan/Tilt and PTZ Units
Motorised devices that move a camera either horizontally (pan), vertically (tilt) or both (pan and tilt). If the lens is also adjustable these are called pan, tilt and zoom (PTZ) units.
Camera positions pre-programmed into the camera PTZ system, often to match an alarm sensors area of coverage.
Transparent hemispherical protective lens/camera housing, often used with PTZ cameras.
A measurement of light levels. CCTV systems are classified according to their ability to operate at particular light levels, e.g.  Daylight; Lowlight; Moonlight; Starlight or Infrared.
Monochrome cameras are generally better than colour in poorer light conditions/infrared.
Light Emitting Diodes (LEDs)
A form of lighting with low energy consumption/ heat output, unlike traditional filament bulbs.
IR Illuminators
Infra-red lighting capability, for dusk/night viewing.
The camera posts or fixings.
Enclosures to protect cameras from the elements. They can be heated, have screen washers and wipers and may be sold as vandal or even bullet resistant.
IP Rating
An international code system for indicating levels of resistance of enclosures to the ingress of dust and liquid.
An electronic sensor for detecting access of people or objects into an area.
Video/Digital Motion Detection (VMD/DMD)
Automated creation of an alarm output via movement noted within an observed image.
Video Analytics (VA)
Creation of an alarm output via changes noted in an observed image, but only after first analysing the change to determine its likely cause – the aim being to sort events requiring action, e.g. human intrusion, from benign background changes, e.g. a tree blowing in wind.
Video/Smoke Detection (VSD)
Fire detection via changes in camera images.
Local Transmission Systems
These transfer the images from cameras to the site multiplexer. Cables are most frequently used, e.g. coaxial (Coax), twisted pair or fibre-optic. Wireless transmission can also be used, as can IP enabled local networks.
Devices that allow an expansion of the number of cameras or detectors, etc, to be connected to a local transmission system.
Internet Protocol (IP) ‘Enabled’ Transmission
Refers to a method of transferring information in digital ‘packets’ between items of CCTV equipment.
Local or Wide Area Networks
LAN/WAN data networks using IP transmission. When IP networks used for other purposes are also used for CCTV, careful attention to network security is required to maintain the concept of a ‘closed circuit’, i.e. secure, CCTV.
These electronic control units combine the outputs from more than one camera for onward transmission to viewing or recording equipment and/or act as the local system control equipment. Multiplexers performing several functions are referred to as Simplex - 1 function or Duplex - 2 functions etc, machines.
Device to select the camera image viewed.
Devices that enable several different images to be displayed on a monitor simultaneously.
Television screen used to view images. Various types exist:

  • Cathode Ray Tube (CRT) monitors – Now regarded as old monitor technology.
  • Liquid Crystal Display (LCD) or Light Emitting Diode (LED) – Current digital technology.  

Matrix Systems
Device that enables images to be switched or shared between different monitors either by manual or automatic control.
Image Recorders
Devices to record images either in real time or in time-lapse (at preset intervals). Two basic types exist:

  • Video Recorders – Now regarded as old recording technology. VHS video tape usually used, but better picture quality can be obtained with Super VHS recorders and tapes.
  • Digital Recorders – Current technology, they come in several types, e.g. Digital Video Recorders (DVR), Digital Versatile Disc (DVD) or Network Video Recorders (NVR). Their advantage over video being the amount of data that can be stored and the speed of information retrieval. As they are derived from computer technology, they can place images on a Hard Disc Drive (HDD) &/or copy or overwrite data to a removable disc (DVD/R or DVD/RW, etc) &/or provide High Definition (HD) image recording/viewing.

Picture Tagging
Electronically marking images with the date and time of the recording.
Real Time
Images are normally recorded at 50 individual frames (pictures) per sec. When played back at this rate, the human eye sees the images as continuous movement.
When more than one camera is in use in a system, the available frames per second being recorded are divided between them.  The time taken for a system to record two pictures in turn from the same camera is known as the cycle time.
In systems with many cameras the cycle time may become long enough for images within a sequence of activity from one camera to not be recorded.
Home Office recommendations are for a maximum cycle time of one second per camera; i.e., in real time recording at 50 frames per second the maximum number of cameras linked to one recorder would be 50. Cycle time is adversely affected by time-lapse recording.
A method for slowing down recording speed, resulting in fewer frames per second being recorded. As longer time lapse periods are selected, cycle time increases and images played back appear less like continuous movement and more like linked photographs.
Time lapse was originally invented to cope with the need for VHS tapes of limited duration (typically 3 hrs) to be left running unattended for long periods, e.g. overnight. When such a recorder is in time lapse mode, the reduction of frames per second recorded is proportional to the extension of recording time. For example, with a 3 hour tape set to record in time-lapse for 24 hours (i.e. tape duration slowed down by eight times), the number of fields per second is reduced by eight, i.e. from the normal 50 to around 6. In order not to exceed the recommended cycle time, in this example the maximum number of cameras linked to one recorder would be limited to 6 not the 50 if possible if recording in real time.
With digital recorders now providing hugely increased data recording capabilities, which may also be coupled with image recording only being instigated by camera image change detection systems, e.g. VMD/DMD, time lapse restrictions are often a less significant issue than they used to be.
Event or Alarm Image Recording
If a CCTV system is automatically activated, relevant camera images of the activating event are stored. Once the link to a RVRC is connected, these event images are passed to the RVRC.
To speed data transmission times, digital information within images needs to be reduced before it is sent to a RVRC. Various protocols exist to enable this without undue loss of picture quality. Well known acronyms are JPEG, Motion JPEG and MPEG 1 and 2.
Refresh Rate
A measure of how often pictures being transmitted to a RVRC are updated.
Frame Overlap
Boosts refresh rates by transmitting only the bits of an image that have changed since the last frame.    
Analogue Transmission
Older process of image scanning and transfer to a RVRC via relatively slow PSTN ‘dial up’ technology.
Digital Transmission
Method of converting analogue information to digital form, DVST and ADPRO being well known examples, before transmission to a RVRC.
Public Switched ‘Phone Network (PSTN)
The analogue UK telephone system.
Integrated Switched Digital Network (ISDN)
The UK digital telephone/data network, now being progressively replaced by ADSL.
Asynchronous Digital Subscriber Line
The ADSL (Broadband) network, often also referred to as the internet or ‘IP’ transmission.
Dual Path Signalling
Signalling to a RVRC via a main route, with a back up route used should the first fail.
Remote Video Response (or Receiving) Centre (RVRC)
24/7 secure manned premises set up to receive and respond to images from CCTV systems.
Unique Reference Number (URN)   
Number allocated by the responding police force to BS 8418 compliant CCTV systems, which enables the RVRC, if they deem it necessary, to request a priority police response to the site.

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Please Note
This document contains general information and guidance and is not and should not be relied on as specific advice. The document may not cover every risk, exposure or hazard that may arise and Aviva recommend that you obtain specific advice relevant to the circumstances. AVIVA accepts no responsibility or liability towards any person who may rely upon this document.

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