Copyright is an exclusive right to the author or maker of the original piece of work. This includes the right to adapt and disribute there work. Copyright cannot protect an idea ,it only can protect the expressinon. Copyright owners have staturtory rights over what to do with there works for a specific period of time after entering the public domain from there onwards the ‘fair use’ law begins which allwos others to use limited copyrighted material without accuiring permission.
Copyleft is playing on the word copyright. It means that using the copyright law you can dispurse modified versions of the work. Only if they reserve the same rights an example would be the GNU (general public license).