Open source means you can see the code and modify it
Open source software is a program where the underlying code — the instructions that make it work — is publicly available for anyone to read, use, and change. When software is open source, the creator publishes the source code instead of keeping it secret. You are not just buying a finished product; you get access to how it was built.
This is different from proprietary software, where the company keeps the code hidden and you only get the finished program. With open source, if you have the technical skill, you can look at exactly what the program does, find problems, fix them yourself, or build something new on top of it.
Open source does not mean the software is free of charge, though many open source programs are. It means the code is open — the licensing model and the price are separate questions. Some open source software costs money. Some is free. The defining feature is that the source code is accessible.
Key Takeaways
- Open source software publishes its source code publicly, so anyone can read it, modify it, and redistribute it under the terms of the license.
- Common open source licenses include the GPL, MIT, and Apache licenses, each with different rules about how you can use and share the code.
- Open source does not automatically mean free — some open source programs charge money, while others are free.
- You can use open source software without modifying it, just like proprietary software, but you have the option to change it if you need to.
- Open source projects are often maintained by communities of volunteers or by companies that release code publicly while offering support services.
How open source licensing works
Open source software comes with a license that spells out what you can and cannot do with the code. The license is the legal agreement that makes it open source. Without a license, the code is not actually open source — it is just code someone published.
The most common open source licenses are the GPL (GNU General Public License), the MIT License, and the Apache License. Each one has different rules. The GPL requires that if you modify the code and distribute it, you must release your changes under the GPL as well — this is called "copyleft." The MIT License is simpler: you can use, modify, and sell the code with almost no restrictions, as long as you include the original copyright notice. The Apache License is similar to MIT but includes explicit patent protections.
When you download open source software, you are agreeing to follow the license that comes with it. If the license says you can modify the code, you can. If it says you must share your modifications, you must. The license is what makes open source legally enforceable.
Why companies release open source software
Large companies like Google, Microsoft, and Meta release open source software for several reasons. Sometimes they use open source code internally and release their own improvements back to the community. Sometimes they release code to build trust or to set a standard that benefits their business. Sometimes they want help from other developers to improve the software faster.
A company might release open source software and then offer paid support, training, or hosting services around it. Red Hat, for example, releases the open source operating system Fedora for free, but sells support contracts and a commercial version called Red Hat Enterprise Linux. The company profits from services, not from selling the code itself.
Open source also reduces the cost of development. When many developers contribute to a project, the work is shared. A company does not have to pay for all the improvements — the community contributes them.
The difference between using open source and modifying it
You do not have to modify open source software to use it. If you download Firefox, LibreOffice, or WordPress, you can use them exactly like proprietary software without ever looking at the code. The fact that the code is open does not require you to do anything with it.
Modifying open source software requires technical skill. You need to understand programming, find the relevant code, make changes, test them, and often rebuild the program. Most people who use open source software never modify it. They benefit from the fact that other developers can modify it and fix problems, but they do not do the modification themselves.
If you do modify open source software, the license determines what you can do with your changes. Some licenses require you to share your modifications with others. Some let you keep them private. This is where the specific license matters most.
Common open source software you may already use
Many widely used programs are open source. Firefox is an open source web browser. LibreOffice is an open source office suite that works like Microsoft Office. WordPress is an open source platform for building websites. VLC is an open source media player. GIMP is an open source image editor. Blender is an open source 3D modeling and animation tool.
The Android operating system is open source, though Google controls the main version. Linux, the operating system that powers most web servers and many devices, is open source. Chromium, the open source project behind Google Chrome, is open source — though Chrome itself includes proprietary components.
You may also be using open source code without knowing it. Many websites and applications use open source libraries and frameworks behind the scenes. A developer might use an open source database, an open source web framework, and open source security libraries all in one application.
Open source versus free software
Open source and free software are related but not identical. Free software is a philosophy that emphasizes user freedom — the freedom to run, modify, and share software. Open source is a practical approach focused on the benefits of publishing source code, like better security and faster development.
Most free software is also open source, and most open source software respects the freedoms that free software advocates care about. But the terms have different meanings. A program could theoretically be open source but not free software, or vice versa, depending on the license.
In everyday use, the distinction rarely matters. When someone says a program is open source, they usually mean it is free to use and modify. When they say it is free software, they usually mean the same thing. The difference is mainly important to people who care deeply about software philosophy.
Security and transparency in open source
One major advantage of open source is transparency. Because the code is public, many eyes can review it and find security problems. If a vulnerability exists, the community can spot it and fix it quickly. This is why open source software is often considered more secure than proprietary software — not because open source code is inherently better written, but because it is auditable.
However, transparency is not automatic security. An open source project with few active developers might have vulnerabilities that go unnoticed for years. A popular project with many contributors is more likely to catch problems quickly. The security benefit depends on how actively the project is maintained and reviewed.
When you use open source software, you can read the code yourself if you have the skill. You can verify that the program does not contain spyware or hidden tracking. With proprietary software, you have to trust the company. With open source, you can verify for yourself.
Frequently Asked Questions
Does open source mean I can use the software for free?
Most open source software is free, but not all. The license determines what you can do with the code, not whether you pay money. Some open source projects charge for downloads, support, or hosting. However, the source code itself is always available to read and modify under the terms of the license.
Can I use open source code in my own commercial product?
It depends on the license. Some open source licenses, like MIT and Apache, allow commercial use with minimal restrictions. Others, like the GPL, require that your product also be open source if you distribute it. Always read the license before using open source code in a commercial project.
What happens if I find a bug in open source software?
You can report it to the project maintainers, usually through a bug tracker on their website. If you have the skill, you can fix it yourself and submit the fix as a contribution. The maintainers decide whether to accept your fix. Most open source projects welcome bug reports and fixes from the community.
Is open source software less reliable than paid software?
Not necessarily. Some open source software is extremely reliable and widely used in critical systems. Others are experimental or poorly maintained. Reliability depends on the specific project, how many developers work on it, and how long it has been maintained — not on whether it is open source or proprietary.
Do I need to know how to code to use open source software?
No. You can use open source software exactly like any other program without understanding the code. The open source license only matters if you want to modify the code or redistribute it. Most users of open source software never look at the source code.