"Free as in beer" vs "Free as in speech"

American software freedom activist, and computer programmer Richard Stallman summarised the difference between Open-Source software and Freeware in a slogan: "Think free as in free speech, not free beer."

Whats that mean?

"Free as in Beer" means Free in the sense of costing no money (gratis). This term and its counterpart "Free as in speech" (libre) are mostly used in computing contexts, as for example when comparing traditional freeware (which may be proprietary) with open-source sotware (where anybody can access and modify the source code).

Here are some links to free software. Some are Libre, all are Gratis.