Free software is software distributed under terms that grant every user four essential freedoms: to run the program for any purpose, to study and change it, to redistribute copies and to distribute modified versions. In software licensing, the word “free” refers to freedom, not price, a distinction often summarized as free as in free speech, not free as in free beer.
The concept was formulated by the Free Software Foundation (FSF) and the GNU Project in the 1980s. Whether a program is free software is decided entirely by its license terms and access to source code, not by whether it costs money, who develops it or how popular it is.
The four freedoms that define free software
The FSF definition numbers the freedoms from zero to three. A program qualifies only if its license grants all four freedoms to every recipient. Freedoms one and three require access to the source code, because studying or improving a program is impractical with only a compiled binary.
| Freedom | What it permits | Practical meaning |
|---|---|---|
| Freedom 0 | Run the program for any purpose | No restrictions on field of use or user |
| Freedom 1 | Study how it works and change it | Source code must be available |
| Freedom 2 | Redistribute copies | Sharing with others, free or for a fee |
| Freedom 3 | Distribute modified versions | Improvements can benefit the community |
Selling free software is fully compatible with the definition. A distributor may charge for copies, support or services, as long as recipients receive the same freedoms. Restrictions such as “non-commercial use only” or “no modification” make a license non-free, even if the source is published.
Copyleft and permissive free software licenses
Free software licenses fall into two broad families. Copyleft licenses such as the GPL require that distributed modified versions remain free under the same terms. Permissive licenses such as the MIT license and the Apache License allow the code to be incorporated into proprietary products as long as notices are preserved.
| License | Family | Key obligation on redistribution |
|---|---|---|
| GPL v3 | Strong copyleft | Whole derivative work under GPL, source provided |
| LGPL | Weak copyleft | Modified library stays LGPL; linking programs may be proprietary |
| AGPL | Network copyleft | Source offered also to users over a network |
| MPL 2.0 | File-level copyleft | Modified files stay under MPL |
| Apache License 2.0 | Permissive | Keep notices, state changes, patent grant included |
| MIT license | Permissive | Keep copyright and license notice |
The FSF itself prefers copyleft, because it guarantees that freedom survives redistribution. Permissive licenses still meet the free software definition; the difference lies in whether downstream distributors may remove the freedoms from their own versions.
Free software compared with related terms
Several terms overlap with free software but are not equivalent. Open source, defined by the Open Source Initiative, covers almost the same set of licenses but emphasizes practical development benefits rather than user freedom as an ethical principle. Freeware only means no charge and usually comes without source code or modification rights.
| Term | Defining criterion | Source code available | Modification allowed |
|---|---|---|---|
| Free software | Four freedoms for all users | Yes | Yes |
| Open source | Open Source Definition criteria | Yes | Yes |
| Freeware | No purchase price | Usually no | Usually no |
| Shareware | Trial before payment | No | No |
| Source-available | Code can be read under restrictions | Yes | Limited or none |
| Public domain | No copyright claimed | Varies | Yes |
The term FOSS or FLOSS (free/libre and open source software) is used to cover both movements neutrally. The word libre is borrowed from Romance languages to avoid the ambiguity of “free” in English.
Using free software in organizations
Organizations use free software extensively, from operating systems and databases to libraries embedded in commercial products. The freedoms bring independence from a single vendor and the ability to audit and fix code, but each license also creates compliance obligations that must be tracked.
| Scenario | Typical obligation | Recommended action |
|---|---|---|
| Internal use only | Usually none beyond the license itself | Record components in an inventory |
| Shipping a product with GPL code | Provide corresponding source code | Prepare a source offer or source archive |
| Running AGPL code as a public service | Offer source to network users | Publish the modified source |
| Bundling permissive libraries | Preserve notices | Include a third-party notices file |
A software bill of materials (SBOM) and automated license scanning make these obligations manageable. Legal review is advisable when copyleft and proprietary code are combined in one distributed product.
Common misconceptions
- Free software is not necessarily gratis; it may be sold, and gratis software is often not free software.
- Publishing source code is not enough; without the right to modify and share, the program is only source-available.
- Free software is not public domain; it remains copyrighted, and the license grants the freedoms.
- Using GPL software internally does not by itself require releasing your own code; obligations arise mainly on distribution.
Explained without jargon
Free software is about what you are allowed to do, not about the price tag. You may use it for anything, look inside to see how it works, change it and share it with others.
Think of a recipe that comes with permission to cook, adapt and pass it on. A free sample of a cake is different. You can eat it, but you do not learn how it was made. Free software gives you the recipe and the rights.
A typical use case
A municipal office needs a document management system and wants to avoid depending on a single supplier. It chooses a free software platform licensed under the AGPL and hires a local company to adapt it to the office’s records procedures.
Because the office has the right to study and modify the code, it can switch to another service company if the first one stops supporting it. The changes are published as source code, as the AGPL requires for a service offered over a network, and two neighboring municipalities later reuse the same improvements instead of paying for them again.