It is a legal right that someone has to intellectual or physical property.
Anything can be copyrighted, and copyright lasts 70 years after the remainder of the creator's life.
The owner has full rights to the copyrighted image, movie, or other media.
Fair Use is the strictures which limit the usage of copyrighted material; however you don't need the owner's permission.
An example of fair use would be using less than 10% of a copyrighted video for a compilation.
Allows people to use content for non-monetary purposes easily.
Public Domain is the area of material that is not restricted by copyright.
Can be easily found and accessed through public databases.
A work can be dedicated to the public domain if an author wants their work to be available to all people.
Everything is a remix
This also has a lot to do with copyright: when people make a remix, the author can choose whether or not to detest the remix for being too close to the original.
"Nothing is original, everything is a remix." -Kirby Ferguson
This issue makes us wonder through: who inspired the original work? Did they get some of their ideas from other artists? Are they then violating another copyright by creating the song in the first place?
People have been stealing other people's work and changing it to be their own for centuries, and it will continue onward in this one as well through remixes and original songs that adapt their melodies from previous songs.