Copyright means "the right to copy". It is the legal right of the author to make copies of and use his/her work.
Before 1989, the author had to give notice under US laws with the letter C to exercise his/her copyright on his/her work. In 1989, the US laws were revised to make copyrights automatically applied to all work of creation. This made ownership of the copyrights easy but sharing difficult as users would need to seek specific permission from the authors to use their work.
To solve the problem, a non-profit organization called the Creative Commons (CC) was formed in 2001 to issue free copyright licences specifying the conditions under which the author would allow public use of his/her work.
[Source of reference: “Copyrights” – Wikipedia December 23, 2012, http://en.wikipedia.org/wiki/Copyright]