1. A somewhat ambiguous term that refers to software that is released with its source code. The fact that the source code is provided does not necessarily mean that users can modify and redistribute the source code. The term is sometimes used interchangeably with "free software", although they are not always the same. (Also, see Public Domain and Shareware.) From I-gloss

2. Term coined in March 1998 following the Mozilla release to describe software distributed in source under licenses guaranteeing anybody rights to freely use, modify, and redistribute, the code. The intent was to be able to sell the hackers' ways of doing software to industry and the mainstream by avoid the negative connotations (to suits) of the term "free software". From Linux Guide @FirstLinux

3. n. [common; also adj. `open-source'] Term coined in March 1998 following the Mozilla release to describe software distributed in source under licenses guaranteeing anybody rights to freely use, modify, and redistribute, the code. The intent was to be able to sell the hackers' ways of doing software to industry and the mainstream by avoid the negative connotations (to suits) of the term "free software". For discussion of the followon tactics and their consequences, see the Open Source Initiative site. From Jargon Dictionary