Explanation/Reference:
Windows Rights Management Services (also called Rights Management Services, Active Directory Rights Management Services or RMS) is a form of Information Rights Management used on Microsoft Windows that uses encryption and a form of selective functionality denial for limiting access to documents such as corporate e-mail, Word documents, and web pages, and the operations authorized users can perform on them. Companies can use this technology to encrypt information stored in such document formats, and through policies embedded in the documents, prevent the protected content from being decrypted except by specified people or groups, in certain environments, under certain conditions, and for certain periods of time.
Reference: http://en.wikipedia.org/wiki/Active_Directory_Rights_Management_Services