Definition of open-source:
(adj) :
(software) Of or relating to software where the source code is freely available and licensed in a manner that permits modification and redistribution.
(adj) :
(by extension) Describing any product whose composition or method of manufacturing is public knowledge and not proprietary.
(v) :
(transitive, computing) To release the source code of, so as to permit modification and redistribution.
(adj) :
(espionage) Relying on publicly available information (open sources).