So, what does open source mean? In the simplest terms, open source describes software whose source code is publicly available for anyone to see, modify, and share. When a program is open source, you are not just allowed to use it, you are invited to look under the hood, fix bugs, add features, and pass your improved version on to others.
The idea powers an enormous share of modern technology. According to Synopsys' 2023 Open Source Security and Risk Analysis report, 96% of commercial codebases contain open source components, and 76% of the code their auditors scanned was open source. GitHub, the largest home of open source collaboration, now hosts more than 180 million developers and 630 million repositories. If you have used a phone, a browser, or the internet today, you have used open source.
Key Takeaways
Open source means software with publicly available source code that anyone can use, study, modify, and share.
The Open Source Initiative (OSI) maintains the official 10-part Open Source Definition, the standard since 1998.
An open source license (MIT, Apache 2.0, GPL) is what legally grants these freedoms; without a license, code is not open source.
96% of commercial codebases contain open source (Synopsys OSSRA 2023); GitHub hosts 180M+ developers and 630M repositories (Octoverse 2025).
Famous examples include Linux, Python, Kubernetes, and VS Code.
What Does Open Source Mean, Exactly?
The term "open source" originally referred to open source software (OSS): code designed to be publicly accessible so anyone can see, modify, and distribute it as they see fit. The meaning has since grown into a way of working: decentralized, collaborative development built on peer review and community production.
Strip away the history and the legal text, and "what does open source mean" comes down to four freedoms:
Use it for any purpose, no permission needed.
Study how it works, because the source code is available.
Modify it to fit your needs.
Share it, including your modified versions, with anyone.
These four ideas are the practical heart of the concept. Everything else, licenses, communities, foundations, exists to protect them.
The Official Definition: 10 Criteria
The formal standard is the Open Source Definition, published and maintained by the Open Source Initiative (OSI), which has shepherded it since 1998. A license only counts as an open source license if it meets all ten criteria:
Free redistribution: the license cannot stop anyone from selling or giving away the software, and cannot demand royalties.
Source code: the program must include source code, or provide a well-publicized way to get it, in the form a programmer would actually modify. Deliberately obfuscated code does not count.
Derived works: the license must allow modifications and let them be distributed under the same terms.
Integrity of the author's source code: the license may require modified versions to carry a different name or version number, so the original author's reputation is protected.
No discrimination against persons or groups: anyone can use it.
No discrimination against fields of endeavor: the license cannot restrict use in a specific industry or for a specific purpose, not even for uses the author dislikes.
Distribution of license: rights apply automatically to everyone who receives the program, with no extra license to sign.
License must not be specific to a product: rights cannot depend on the program being part of a particular software bundle.
License must not restrict other software: the license cannot insist that other programs shipped alongside it also be open source.
License must be technology-neutral: no provisions tied to a specific technology or interface style.
Why does this level of precision matter? Because "open source" is not a vibe, it is a standard. When a company claims its product is open source, these ten criteria are the test.
Open Source Licenses: The Rules That Make It Real
Here is the part most explainers gloss over: source code being visible is not enough. What legally makes software open source is its license. Without an OSI-approved license, code on the internet is just visible, not open source. As Red Hat's participation guidelines note, software that is not under an open source license is not open source, even if it is developed in the open.
The three licenses you will meet most often:
License | Type | What it means in practice |
|---|---|---|
MIT | Permissive | Do almost anything, including building closed-source products on top of it; just keep the copyright notice. |
Apache 2.0 | Permissive | Like MIT, plus an explicit patent grant from contributors. |
GPL (v2/v3) | Copyleft | You can modify and share, but distributed derivatives must stay open under the same license. |
Permissive licenses (MIT, Apache 2.0) maximize reuse, including inside proprietary products. Copyleft licenses (GPL) maximize openness: improvements must be shared back. Neither is "better" in the abstract; they encode different philosophies about freedom.
Open Source vs Free Software: Is There a Difference?
You will often see "free software" used as a synonym, and the confusion is historic. What we now call open source was originally called "free software," where "free" meant liberty, not price. As the term spread, the ambiguity of "free" caused endless confusion, so on February 5, 1998, at a meeting at VA Research, Christine Peterson proposed the term "open source" for software with available, modifiable, shareable source code.
Today the two movements mostly agree on which licenses qualify. The Free Software Foundation maintains its own 4-part Free Software Definition, and both organizations interpret their definitions when judging licenses. The practical difference is emphasis: free software stresses user freedom as an ethical imperative, while open source stresses the collaborative development model and its practical benefits. For most developers choosing a license, the distinction rarely changes the outcome.
Why Open Source Matters: The Numbers
Open source is not a niche hobby; it is the substrate of the software industry:
96% of commercial codebases contain open source components, and 76% of scanned code was open source (Synopsys OSSRA 2023).
180 million+ developers build on GitHub, with 36 million+ joining in a single year, more than one every second (GitHub Octoverse 2025).
630 million repositories live on GitHub, with roughly 230 new ones created every minute.
The values of collaboration and peer review were written into the internet's foundations: early ARPANET researchers shared and built upon one another's source code (Red Hat).
The business case follows from the model. Open source software is often cheaper and more flexible than proprietary alternatives, and it tends to outlive single vendors because communities, not companies, maintain it. When a proprietary product is discontinued, it dies; when an open source project's sponsor leaves, the community can fork it and continue.
Famous Open Source Examples
You probably use open source every day without noticing:
Software | What it is | License |
|---|---|---|
Linux | The operating system kernel running most servers and Android phones | GPLv2 |
Python | The programming language behind much of AI and data science | PSF License |
Kubernetes | The container orchestration platform running modern cloud infrastructure | Apache 2.0 |
VS Code | Microsoft's popular code editor | MIT |
Blender | The 3D creation suite used by studios and hobbyists alike | GPL |
How to Get Started with Open Source
Use it. Pick an open source tool for a real task: VS Code for editing, Blender for 3D, LibreOffice for documents.
Read code. Find a project you use on GitHub and read a small part of it. Reading real code is the fastest way to understand the definition in practice. If you want quick video breakdowns of trending repos, browse the repo signals for 30-second overviews.
Contribute. Start with documentation fixes or good-first-issues. Most projects label beginner-friendly tasks.
Publish your own. Put a side project on GitHub with an OSI-approved license. GitHub's own choosealicense.com walks you through the choice.
Frequently Asked Questions
Is open source software free?
Usually, but "free" is not the point. Open source is about freedom, not price: the freedom to use, study, modify, and share. Most open source software costs nothing, but a license can legally allow selling it (criterion 1 of the Open Source Definition explicitly permits selling). Companies like Red Hat built large businesses on support and services around free-to-download open source software.
Can companies make money from open source?
Yes, and many do. Common models include paid support and services (Red Hat), hosted cloud versions, dual licensing, and enterprise features. Making money from open source does not violate its principles; restricting users' freedoms would.
Is open source secure?
Visibility cuts both ways. Anyone can review open source code, which means bugs get found and fixed by the community, but attackers can also study it. The Synopsys OSSRA 2023 report found 84% of audited codebases contained at least one known open source vulnerability. The lesson: open source is not automatically secure; keeping dependencies updated is essential.
Who owns open source software?
The contributors collectively, under the terms of the license. Copyright still exists; the license is what grants everyone else rights. That is why the license matters more than the visibility of the code.
What does open source mean for AI?
The OSI released the Open Source AI Definition in October 2024, extending the same principles to AI systems: users must be able to use, study, modify, and share the system, covering model code, parameters, and training data information. "Open weights" alone, without training data transparency, does not meet the bar.
How is open source different from freeware?
Freeware costs nothing but keeps its source code closed: you cannot study or modify it. Open source gives you the code and the legal right to change and share it. Price and openness are independent axes.
Conclusion
What does open source mean? It means software you are free to use, study, modify, and share, protected by a license that meets the Open Source Initiative's ten criteria. It is the reason a student can download the same tools as a large company, the reason 96% of commercial software contains community-built code, and the reason the internet itself exists in its current form.
If you take one action after reading this, make it small: find one open source tool you already use, visit its repository, and read its license file. You will be looking at the legal text that keeps the whole ecosystem open.