There are a few definitions. The FSF has one http://www.gnu.org/philosophy/free-sw.html http://www.gnu.org/philosophy/free-sw.html the OSI has one http://openso

There are a few definitions. The FSF has one http://www.gnu.org/philosophy/free-sw.html http://www.gnu.org/philosophy/free-sw.html the OSI has one http://opensource.org/osd-annotated http://opensource.org/osd-annotated Debian has one http://www.debian.org/social_contract#guidelines http://www.debian.org/social_contract#guidelines They are nearly all extactly the same. Another defintion is if the code is released under and OSI approved "open source licence" (http://opensource.org/licenses/alphabetical http://opensource.org/licenses/alphabetical ) or an FSF approved "free software licence" ( http://www.gnu.org/licenses/license-list.html http://www.gnu.org/licenses/license-list.html ). Again AFAIK, nearly exactly the same.