Copyright is a protection that the federal government gives to authors for their original works. Original works of authorship include literature, music, visual art and other art forms, published or unpublished. Copyright laws give to the original creator of a work the right to decide how it is distributed or reproduced and various kinds of copyrights exist.
The United States Copyright Office, in its document "Copyright Basics," defines copyright as a protection granted to authors of originals works. It allows them to do with their works whatever they want and requires others to get permission from the author to use those works. These regulations protect an author's rights to decide whether or not other people can reproduce copies, base other works upon that author's work, distribute copies of the work, perform the work publicly or display the work publicly. A work that has copyright is usually followed by the word "Copyright" or the copyright symbol (©).
There are not several types of copyrights. Copyright is a law that gives people protection to their works. However, copyright rules provide the author with various types of situations and decisions he can make regarding his copyrighted works. For example, he can decide whether or not to share his work or the extent to which others may reproduce it.
GNU is a type of license that applies to copyrighted works that have a notice from the copyright holder that says the work can be distributed under the terms of a GNU license. This notice grants a worldwide and unlimited duration to use that work under certain conditions, such as making copies of the work. If you make copies, modify the work or distribute it in a way, that requires permission, and under copyright law, you are accepting this license.
Example: Creative Commons
Creative Commons (CC) is a non-profit organization that helps to facilitate the sharing of works and the building of new works that are partially based upon existing copyrighted works. CC provides free licenses to use copyrighted works whose author has allowed some public use. As an author, you can use CC to change your works from "all rights reserved" to "some rights reserved" and allow others to have use of your works. This is not an alternative to copyright or a different type of copyright, as it works with copyright laws, opening the possibilities of usage of a work.
Example: Public Domain
Public domain is the term that refers to works that are not eligible for copyright or for which copyright protection is no longer available. Anyone wishing to use, reproduce or distribute a work in the public domain may do so without needing to seek permission from the owner.