What is the difference between a fixed work and a work that is not fixed?

In the context of copyright law, a work is considered to be fixed when it is embodied in a tangible, stable, and concrete form. For instance, a short story that is printed on paper meets this requirement, while a live performance of the same short story that is not being simultaneously recorded does not. The Copyright Act of 1976 requires that in order to meet the standards of copyright law, works of authorship must be embodied in a form that is sufficiently permanent to be reproduced, communicated, and perceived. Consequently, works that are transitory in nature are not protectible under copyright law, since they are not fixed.

To illustrate the difference between a fixed work and a work that is not fixed in a practical scenario I will consider a real situation involving a university professor and a graduate student regarding the copyrights of lecture materials and associated class notes. A personal friend of mine completing graduate studies had been taking excellent class notes during lectures and creating thorough course guides by complementing the class notes with materials from additional sources and using a professional quality typesetting system to publish them. Additionally, the student decided to make these course guides freely available to other students as PDF documents. I recently learned about a dispute involving the copyrights of the lecture materials between the university professor and the student. The dispute goes as follows. Allegedly, the university professor wanted to prevent the student from sharing her course guides with other students on the basis that since the student had created them based on her lectures, she -as the professor-- was the copyright owner of the materials.

Analyzing the previous case, we find that based on the US Copyright Act of 1976 and the Berne Convention Implementation Act, the student not only is within her right to distribute the course guides as she pleases without any copyright infringement, but also has the right to seek copyright protection for her work of authorship. Given that the professor lectures have not been simultaneously taped or transcribed, they are transient in nature and cannot be protected by copyright laws since they do not meet the fixation requirement. On the other hand, the student's work of authorship meets the originality, fixation, and Judge Learned Hand's abstraction tests. Additionally, copyright protection does not extend to the ideas, but only to the author's unique expression of the ideas. Consequently, in this particular case the student has the right to copyright the course guides or make them public domain.

References:
[1] Stim, R. "Intellectual Property. Patents, Trademarks, and Copyrights" West Legal Studies.
[2] Black's Law Dictionary 5th ed., (West Publishing, 1979).