Fair use is one of the exceptions in copyright which allows use of copyrighted materials without obtaining permission as long as the use can be considered fair. There is a four-factor analysis which must be applied to each use to determine whether the use is fair. Each factor is given equal weight. The goal is to achieve a balance between the rights of the copyright holder with the rights of the public. Fair use is also technologically neutral so the same analysis may be applied to any medium.
See the link provided below for more information on Copyright & Fair Use