This is a requirement for a work of authorship to be able to be registered and be protected by a copyright. Ideas are not copyrightable. The work must be recorded or embodied in some reproducible medium such as on paper, an audio or video tape, a compact disk or even in a standard digital file store on a USB drive. When it can be reproduced from storage, even with the aid of a machine, the work is said to be fixed in a tangible medium of expression.)