CCTV is short for "closed-circuit television." In the US, CCTV is primarily used for surveillance cameras for businesses. In Europe, CCTV is incorporated into policing, with the downtown areas of cities in some countries wired with cameras.
What is CCTV?
At its core, CCTV is a video system designed to only be viewed by particular users; the picture is not broadcast, but recorded or viewed on a specific monitor. Originally, CCTV was designed for use in banks and casinos. The signal recorded by the cameras is transmitted in a scrambled form to a receiver that unscrambles it. CCTV refers to a method of transmitting any television signal, but the term is most commonly used to refer to surveillance cameras.
As mentioned, CCTV is most commonly used for surveillance. Most major institutions, such as banks or schools, have CCTV networks to reduce the need for human security. Prisons use CCTV for monitoring behaviour from a central location in addition to regular patrols. Video taken with CCTV can be recorded and reviewed later.
CCTV has other practical applications beyond surveillance and CCTV networks don't necessarily feature security cameras. Any kind of on-site video technology uses CCTV, such as a video conference that is only accessible for a select audience.