Libre /ˈliːbrə/ is a loan word in English, borrowed from French and Spanish, used to describe something as being "free", in the sense of "having freedom" or "liberty". It is used in English to distinguish the two meanings of free: free as in freedom (libre) from free as in free of charge (gratis). Another sample is common: Free as "Free Speech", not as "Free Drink"!
Historically the word has been borrowed from Romance languages, usually to refer to free will or freedom of expression in some aspect of the lending culture (e.g. vers libre in French poetry, or the Spanish term Lucha libre, a style of wrestling).
In the 1990s, libre was proposed as an alternative term for free software which avoided the ambiguity in the word "free" in English. The word gained some acceptance in the software community, though the terms "free software" and "open source software" remain dominant. "Free" and "open" have both been rigorously defined in the free software and the open source definitions which have formed the basis of similar definitions in the realms of education, knowledge and culture.
The word "libre" is now used in discourses requiring an unambiguous adjective meaning "free as in freedom", often concerning one or more of the following: open source or open source software, free software, the free software movement or the free culture movement, open and libre knowledge.