HDCP stands for High-bandwidth Digital Copy Protection, which is an additional encryption on HDMI cables used by manufacturers to prevent piracy. It is used by manufacturers of high-definition content like Blu-ray disc players, to prevent playback from unauthorized devices, such as computers and audio/video receivers, so they only play video or sound coming from the player. If a signal is not HDCP compliant, it is stripped away, and prevented from being shown on your display device.