DRM is the weapon against piracy of copyright information, a popular subject with writers and sometimes less popular with consumers. Just as you are supposed to pay for MP3 files nowadays, this is also true for ebooks.

Digital Rights Management
DRM is short for Digital Rights Management. DRM is a special technology which makes it possible to manage copyrights of, for instance, text, music and visual material. With this technology, rightful claimants can determine and restrict the exetent and nature of use.

User agreement
DRM systems are always linked to user agreements, which are governed by contract law and consumer law. This agreement indicates the limitations of the use of, for example, an ebook. A publisher, for instance, can permit only a limited number of copies or iTunes can lay down that a piece of music may only be listened to a certain number of times. The remarkable thing is that consumers often have no idea of the limitations resulting from the acceptance of the user agreement.