Before the term "open source software" was introduced in 1998, software with the appropriate license provisions was termed "free software." The definition of free software (http://www.gnu.org/philosophy/free-sw.html [1]) therefore largely corresponds to that of open source software. In terms of license law, the expressions are equivalent. However, the Free Software Foundation places great value on the term "free software" since they would like to stress the aspect of freedom. Which of the two terms one prefers is therefore more a question of taste and partisanship.