Open Source Software
Open Source Software is defined as software that can be copied and changed by the user. In the beginning free (libre) software was the only kind available after that came proprietary (not free) software and now the software industry is thinking of bringing back free software again. Open source software (OSS) was used for 30 years from 1970 to 2000, however before this time it was something that was taken for granted because almost all the software back then was open source. Throughout the years it became a widely used movement which produced some of the most commonly used software packages in history.
Sources:

http://www.timr.ca/RecentArticles/Online/terminology.html

http://digitalcommons.uconn.edu/cgi/viewcontent.cgi?article=1009&context=libr_pubs