HDCP has to do with digital rights management protocols, which exist to protect content creators against piracy. There are different protocols for different companies and industries, but premises remain the same: DRM blocks some purchases you make for yourself and your devices. If you make a movie purchase on iTunes and you are allowed to play it only on devices with your account, you have DRM protection.
Developed by Intel, HDCP is used with many other digital video standards besides HDMI, such as Digital Visual Interface and DisplayPort. What does it do? – It provides an encrypted connection between a Blu-ray player, streaming device or other content output device on one end and a receiving device (such as an HDTV or audio receiver). HDCP is everywhere and is embedded in most devices we use these days, such as Blu-ray players or satellite TV receivers, as well as on streaming video devices such as Chromecast or Amazon Fire TV. It is also embedded in laptops, DVRs and other HDMI cable devices.
Unfortunately, HDCP may also be a nuisance, because it often prevents consumers from doing legal things with their content and devices. For example, if a chain device is not HDCP compatible, the video stream will fail.