What is it?
Copyright is about protecting creators. Whenever someone creates something new by putting pen to paper, choreographing a dance, designing a graph, or taking a photo it is theirs from the moment of its creation forward. And the creator's rights to benefit from that work (literary, artistic, musical, dramatic, written or unwritten) financially or otherwise is protected by law.
Copyright law protects authors from having their works copied without their permission. (Title 17 of the United States Code; Copyright Act of 1976).
When the creator of a work dies, the rights to benefit from a work passes to his/her family and continues for 70 years after the creator's death; at that point, the work enters the 'public domain.'