According to the Merriam-Webster Dictionary, copyright "is the exclusive legal right to reproduce, publish, sell, or distribute the matter and form of something (such as a literary, musical, or artistic work."
Copyright isn't straight forward, but is very complex. It is divided into three parts: copyright, fair use, and public domain.
Copyrights are granted for the life of the author, plus 70 years. For corporations, it's 95-120 years past the creation date.
However, some copyright items can be used under fair use policy.
Other items might be in the public domain, meaning they are no longer copyrighted.