What Is CopyLeft?
The simplest way to make a work free is to put it in the public
domain, uncopyrighted. This allows people to share the work and
their improvements, if they are so minded. But it also allows
uncooperative people to convert the work into a proprietary work
that they can claim as their own. If it is distributed as an
original work by this new author, people who receive the slightly
modified work do not have the freedom that the original author
gave them; the middleman has stripped it away.
What CopyLeft accomplishes, is a legally binding form of protection
from these opportunistic middlemen, by (1) requiring the author to
copyright his work, and (2) subsequently licensing that copyrighted
work in such a way, that anyone can use it, modify it, distribute
it, in anyway they see fit, with certain restrictions, that insure
that anyone recieving such a work, is fully aware if their rights
covered by this license, and who the original author was, as well
as any additional authors that added to the work along the way.
CopyLeft was originally created for Software, but it wasn't long
before the need was seen to include other works as well. This is
intended to be a very short answer, to very complex subject strewn
with legalese. If you have further questions about your rights
under CopyLeft please go to the following sites...
http://www.fsf.org/
http://dsl.org/copyleft/dsl.txt
http://www.gnu.org/philosophy/license-list.html
Note: I refrained from placing an "a href", html speak for clickable
offsite link, because I am trying to minimize tracking down dead links,
I may revise this thinking after I write a perl script to automatically
perform a dead link check, but for now you'll have to scoop them.