Free software (free software in English, this designation is also sometimes confused with two-way free for the free English in Castilian) is the name of the software that respects the freedom of users to their product purchased and, therefore, a once obtained can be used, copied, studied, changed and redistributed freely. According to the Free Software Foundation free software refers to the users' freedom to run, copy, distribute, study, modify and distribute the modified software.

Free software is often available free or at cost for distribution through other means, but it is not mandatory and therefore must not associate free software "free software" (commonly known as freeware) since, preserving its free, can be distributed commercially (commercial software). Similarly, the "free software" or "free" sometimes includes the source code, however, this type of software is not free in the same sense as free software, unless it guarantees the rights to modify and redistribute such modified versions of the program.

Free software not to be confused with "public domain software. The latter is software that does not require licensing for their exploitation rights are for all humanity, because it belongs to everyone equally. Anyone can make use of it, provided for lawful purposes and leaving their original authorship. This software would be one where the author gives to humanity or whose copyrights have expired, after a longer period after the death of this, usually 70 years. If an author makes its use under a license, however weak it is no longer in the public domain.