Copyright (United States)
Legal rights dictating the ownership and use of media. Copyright laws generally function by prohibiting unauthorized duplication, derivation, distribution, performance, and display of media, although they do not protect the specific concepts or facts contained within that media. However, pursuant to Copyright Law Section 107, both parodies and critical analyses are explicitly exempt from the prohibition against using copyrighted media without permission.
As an example, copyright laws prohibit the duplication character of Harry Potter, but this does not mean the use of a male wizard in other works would also be prohibited, provided that there were significant differences between the two characters. A TV comedy sketch could use the name "Harry Potter" if it were unambiguously part of a parody, and a book about magic in popular culture could use an image from a Harry Potter film if it seemed legitimately warranted.
The "Copyright Clause" of the United States Constitution reads as follows: "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."  Information, unlike material goods, has a zero marginal cost (Benkler 84). it doesn’t cost anything to distribute the information once it has been created, aside from bandwidth space. The only cost inccured is the time it took someone to write something or create something. Copyright is the only thing that allows us to charge for something that costs nothing to “fabricate” and “distribute,” because it establishes that the uniqueness of the ideas and the time that goes into them are worth money. Copyright is essentially an incentive to create, which is discussed in one of Lawrence Lessig's Blogs.
The specific rights consistent with this clause have varied over the last two centuries as legal challenges have continually shaped the scope of copyright powers. Aside from the continually expanding duration of a copyright after the death of its author, we no longer have to register our creative materials with the copyrights officer. All creative material is by default copyrighted the moment you create it.