The document discusses CCTV (closed-circuit television) systems. It describes the basic components of a CCTV system including cameras, lenses, monitors, and DVRs (digital video recorders). It outlines different types of CCTV systems such as wired and wireless. It also discusses various types of CCTV cameras like indoor, outdoor, IR, dome, bullet, and PTZ cameras. Finally, it notes some common applications of CCTV systems like monitoring bars, parking lots, hospitals, and schools.