What is copyright?

In the United States, the idea for Copyright was embedded in the U.S. Constitution in Article 1, Section 8, which describes the powers of Congress. 

"Congress shall have Power...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"

According to U.S. Copyright Law, copyright protects works of original authorship that are fixed in a tangible expression. This includes broad categories of literary works, musical works, dramatic works, visual (pictorial, graphic, and sculptural) works, pantomime and choreographical works, motion pictures and other audiovisual works, sound recordings, and architectural works. Copyright takes effect immediately once a work has been fixed in a tangible form - registration is not necessary - and lasts for 70 years after the death of the author, or, in the case of works for hire or anonymous/pseudonymous works, 95 years from publication or 120 years from creation, whichever is shorter.

Copyright gives the author the following exclusive rights:

• to reproduce the work
• to prepare Derivative Works based on the work
• to distribute the work
• to publicly perform the work
• to publicly display the work

What is NOT protected by copyright?

• works that are not fixed in a tangible form (for example, an improvised performance that is not recorded)
• names, titles, short phrases, slogans, mere listings of ingredients or contents, familiar symbols or designs, mere variations of typography, coloring or lettering
• ideas, procedures, methods, systems, processes, concepts, principles, discoveries, or devices, as distinguished from a description, explanation, or illustration
• works consisting entirely of information that is common property and containing no original authorship (for example: standard calendars, height and weight charts, tape measures and rulers, and lists or tables taken from public documents or other common sources)
• works produced by the U.S. Government

From "Copyright Basics"(pdf), U.S. Copyright Office Circular 1