“Fair use” is a legal term that does not necessarily mean what people often assumes it means (a free pass to use other people’s intellectual property). Indeed, the term has two different meanings, depending on whether copyrights or trademarks are at issue.
Copyright protects works of authorship. See Copyright Protection in One Easy Lesson. The copyright owner has the exclusive right (as applicable) to reproduce, distribute, publicly perform, publicly display, and make derivative works of the copyrighted work.
Copyright infringement is the unauthorized exercise of one of the exclusive rights by someone other than the copyright owner. Thus, for example unauthorized copying of someone else’s music or movie constitutes copyright infringement.