Free software or software libre 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 minimal restrictions only to ensure that further recipients can also do these things. In practice, for software to be distributed as free software, the human readable form of the program (the "source code") must be made available to the recipient along with a notice granting the above permissions. Such a notice is a "free software licence", or, in theory, could be a notice saying that the source code is released into the public domain.
The free software movement was conceived in 1983 by Richard Stallman to make these freedoms available to every computer user. From the late 1990s onward, alternative terms for free software came into use. "Open source software" is the most common such alternative term. Others include "software libre", "free, libre and open-source software" ("FOSS", or, with "libre", "FLOSS"). The antonym of free software is "proprietary software" or non-free software.
Free software is distinct from "freeware" which is proprietary software made available free of charge. Users usually cannot study, modify, or redistribute freeware.
Since free software may be freely redistributed, it generally is available at little or no cost. Free software business models are usually based on adding value such as support, training, customization, integration, or certification. At the same time, some business models which work with proprietary software are not compatible with free software, such as those that depend on a user having no choice but to pay for a licence in order to lawfully use a software product.
