Ever since the creation of video cassette recorders (VCR) movie studios have been utilizing various encryption methods for protecting their content. Encryption means there is a layer of technology on the content media which is intended to thwart copying of the movie. With content as valuable as the Blu-ray format, studios have continued to try to make it very difficult to copy discs for personal use, layering Blu-ray discs with an ever changing encryption scheme attempting to prevent you from creating a copy of a movie you rightfully purchased.
Decrypt means reading the disc and removing the copy protection. This allows you to copy the movie to an alternative storage location such as another disc, a hard drive, or a flash drive. Once the movie is decrypted, it is unprotected and you can do with it what you wish. With the decrypted movie on your hard drive, you can then put it on your laptop or server, and play it anywhere you wish by using compatible Blu-ray software. Arcsoft Total Media Theater, for example, allows you to play a Blu-ray movie stored on your hard drive.
In addition to the commonly known reason for decrypting to copy to a hard drive there are other benefits such as being able to play on a non-HDCP-supported display. If you have an older display or television that is not HDCP-compliant, then the Blu-ray player software will prevent you from being able to watch. Being able to decrypt the movie allows you to watch it anywhere, and on any device.
Unfortunately, there is presently no sponsored software provided by the movie studios which allows you to decrypt a movie for your own personal use. Fortunately, a small company by the name of Slysoft offers a program called AnyDVD HD which allows the decryption of a blu-ray disc (or DVD for that matter) for playback as well as for copying to your hard drive. The program will decrypt movies on the fly in the background, or can be used to copy the movie to a hard drive. As I mentioned, the movie studios do continue to update their copy-protection scheme, so Slysoft does their best (and they are quite fast) at releasing updates to AnyDVD to allow for decrypting of the latest movies.
See How to Back-up a Blu-ray Movie for details on how to use AnyDVD to your advantage.