1984: COPYLEFT
[Overview]
The term "copyleft" was invented in 1984 by Richard Stallman, who was a computer scientist at MIT (Massachusetts Institute of Technology). "Copyleft is a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well. (…) Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. Copyleft guarantees that every user has freedom. (…) Copyleft is a way of using of the copyright on the program. It doesn't mean abandoning the copyright; in fact, doing so would make copyleft impossible. The word 'left' in 'copyleft' is not a reference to the verb 'to leave' — only to the direction which is the inverse of 'right'. (…) The GNU Free Documentation License (FDL) is a form of copyleft intended for use on a manual, textbook or other document to assure everyone the effective freedom to copy and redistribute it, with or without modifications, either commercially or non commercially." (excerpt from the GNU website)