Definition of Libre Software

Libre Software is defined as the freedom for users to use, study, copy, modify and redistribute software as legally guaranteed by its licence.

These liberties are defined by the Free Software Foundation as follows:

  • Liberty 0: The liberty to run the program for any purpose
  • Liberty 1: The liberty to study how the program works
  • Liberty 2: The liberty to redistribute copies of it
  • Liberty 3: The liberty to improve a program and publish its modified versions

Libre Software is protected by copyright. Its specific feature is that the author exercises this right by distributing the software under a Libre license, which defines the user’s rights and obligations. Examples of this are GPL, BSD and CeCILL Libre licenses.

Note also that the term “Software” may be an analogy for the term “Technology”.
See also Wikipedia's definition.

Free Software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients have the same rights under which it was obtained and that manufacturers of consumer products incorporating free software provide the software as source code. The word free in the term free software refers to freedom (liberty) and is not at all related to monetary cost. The Free Software Foundation advises people to "avoid using terms like 'give away' or 'for free,' because those terms imply that the issue is about price, not freedom. Free software is generally available without charge.