Initialism of closed circuit television.
"The security guard monitored the live feed on the cctv screen to detect any suspicious activity in the parking lot."
In plain English: CCTV is short for closed-circuit television, which refers to security cameras that record video of specific areas without broadcasting it publicly.
"The security guard checked the CCTV footage to see who entered the building earlier today."
Initialism of China Central Television.
"The news broadcast was aired on CCTV, which stands for China Central Television."