Definition:
Closed-circuit television (CCTV) is the use of video cameras to transmit a signal to predefined set of monitors. CCTV is often used for surveillance in areas which need security, such as banks, casinos, and airports or military installations.
In industrial plants, CCTV equipment may be used to observe parts of a process that are remote from a control room, or where the environment is not comfortable for humans. CCTV systems may operate continuously or only as required and can be trigered by detected motion or by alarm switch.

Use:
CCTV for use outside government special facilities was developed as a means of increasing security in banks. Today it has developed to the point where it is simple and inexpensive enough to be used in home security systems, and for surveillance. Claims that they reduce or deter crime have not been clearly borne out by independent studies, though the government claims that when properly used they do result in deterrence, rather than displacement. One clear effect that has been noted is a reduction of car crime when used in car parks. Cameras have also been installed in taxis to deter violence against drivers, and also in mobile police surveillance vans.
The most measurable effect of CCTV is not on crime prevention, but on detection and prosecution.

A CCTV system may be installed where an operator of a machine cannot directly observe people who may be injured by unexpected machine operation. For example, on a subway train, CCTV cameras may allow the operator to confirm that people are clear of doors before closing them and starting the train. Operators of an amusement park ride may use a CCTV system to observe that people are not endangered by starting the ride. A CCTV camera and dashboard monitor can make reversing a vehicle safer, if it allows the driver to observe objects or people not otherwise visible.

Many cities and motorway networks have extensive traffic-monitoring systems, using closed-circuit television to detect congestion and notice accidents.

Basic components:
All CCTVs have 2 major components with some variations.
First it require one or more camera, they classified as indoor and outdoor, depending on use requirements, each of these can be divided into color(C) and black and white (BW) categories. Each of those consequeently can be divided into with infrared ot without. Many cameras have exchangeable lenses. Important specs of every lens are: focal length, field of view, resolution, light level. Camera also can be wired or wireless.
Second it requires recording unit. Historically most popular was VCR recording, but recently more any more people find DVR (Digital Video Recorder) to be a better option. DVR contain hard driver and capable of storing much more data. DVR can be either standalone or PC (personal computer) based.

Facts:
* Estimated number of surveillance cameras in private premises in London is around 500,000 and the total number of cameras in the UK is around 4,200,000. The UK has one camera for every 14 people.
* in 1998 New York had over 3300 camera and Chicago 2200.