Copyright, "is a form of protection grounded in the U.S. Constitution and granted by law for original works of authorship fixed in a tangible medium of expression. Copyright covers both published and unpublished works." - U.S. Copyright Office
Put simply, U.S. law provides authors of creative and intellectual works the exclusive "right to copy" their work. This includes the rights to:
Copyright exists from the moment a work is created and put in a tangible medium. This means that copyright does not protect an idea or the facts upon which an idea is based.
In order to re-use a copyrighted work, your use must fall under one of the copyright exceptions laid out in U.S. law or you must ask for permission from the author.
Copyright protects nearly all creative and intellectual works, including (but not limited to):
Copyright law does not protect works that are:
The length of copyright protection depends on several factors, including if the work is published or un-published and when it was created.
Determining the length of copyright protection can sometimes be tricky as U.S. copyright law has changed over the years.
For published works created today, the length of copyright protection is the life of the author plus 70 years. The length of protection could vary, however, depending on if the work was a "make for hire" (i.e. works created by an employee during the course of their job duties), if the work is not published, or if the work was created before 1978.
Length of copyright protection could also vary depending on the laws of the country in which it was created.
When copyright protection expires, that work enters the "public domain" and can be freely used for any purpose without permission.