Copyright is one of three types of intellectual property. Intellectual property also covers patents, which are protections for a process, and trademarks, which protect a brand. Copyright is the original and most pervasive form of intellectual property.
Copyright is the protection of an expressed idea. To be more specific, copyright protects "original works of authorship fixed in a tangible medium of expression. Copyright covers both published and unpublished works" (U.S. Copyright Office, Copyright in General (FAQ)). What does this mean?