Copyright is a form of protection grounded in the U.S. Constitution and granted by law. It is meant to encourage creative work by guaranteeing the creator of the work the right to profit from that work. It protects creative works of original authorship* that are fixed in a tangible medium of expression*. Copyright protects such works as literary, dramatic, musical, and artistic works, including poetry, novels, movies, songs, computer software, and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed.
*Original authorship: The original creator holds the copyright permissions exclusively unless:
-they created the work collaboratively (in which case all authors/creators own the copyright)
-they signed those rights away, either through dedication or in a publishing agreement
*Fixed in a tangible medium of discovery means that it has to be physically located somewhere (it can't be an idea, for example, unless it's written down somewhere).
For more information, see https://www.copyright.gov/help/faq/faq-general.html