Definition
Open source is a way of sharing software in which the source code, the blueprint of a program, is made public so anyone can freely view, modify, and redistribute it. It is also a huge culture of collaboration, where developers and researchers around the world work together to improve programs.
The Chef Who Doesn't Hide the Recipe
Imagine a neighborhood restaurant famous for its stew posts its secret sauce recipe online for everyone. Customers can recreate the taste at home. Someone who loves spicy food can add hot peppers and invent a brand-new dish.
The same thing happens in the software world. In the past, companies kept their source code a closely guarded secret. Source code is the blueprint, written in a programming language, that makes a program work. Without it, outsiders couldn't see how a program worked inside, and they couldn't fix even a tiny glitch themselves.
The open source movement opened that blueprint to the world. Students learning to program can read high-quality code and build their skills quickly. Other programmers can add great features and create even better software.
Collective Intelligence: Developers Around the World Building Together
Even the biggest tech company has a limited number of employees. But when individual developers all over the internet, along with developers from many different companies, put their heads together, they can sometimes solve complex problems that one company could barely handle alone.
When someone spots a flaw or an error (a bug) in a program, another engineer on the other side of the planet may write a fix and send it back to the original author. This kind of participation is called a code contribution. With so many hands helping, projects can gain amazing speed of progress and stability.
In fact, the code underlying the Android operating system on your smartphone, the Linux servers that keep websites running worldwide, and many of the tools behind cutting-edge AI research are all open source. Sometimes one company leads the work and still releases the code, as with Android. However, some apps and services bundled with phones are not public. Open source serves as a solid cornerstone of modern digital life.
To Be More Precise: Freedom With Rules
Open source shares things freely, but that doesn't mean there's no copyright or that you can do whatever you like. Every open source program comes with a set of usage rules, called a license, set by its creator.
For example, some rules are fairly relaxed, like "If you use this program, you must credit the original author" (the MIT License). Others, like the GPL, impose a strict duty to share: "If you distribute a program built from this code, you must also release your changes."
In the end, the freedom in open source isn't about doing whatever you want without responsibility. It only works when it rests on mutual trust and agreement: respecting the rights of those who shared their knowledge first, and enjoying what everyone built together.
Common misconceptions
Because open source code is public, it's easy for hackers to break into.
Public code isn't automatically easier to break into. In projects that many people review, vulnerabilities can be found and fixed quickly. But in projects with few maintainers, old flaws like Heartbleed can go unnoticed for a long time.
Open source is free software, so there are no legal rules.
Even if it's free to use, breaking the license rules set by the original author, such as giving credit or, under some licenses, releasing your modified code, can lead to legal trouble such as copyright infringement.
Where you meet it
The Android operating system, used on the majority of smartphones worldwide, is built on Linux, which is open source.
Python, a programming language widely used for data analysis and AI development, and the Firefox web browser are also well-known open source projects.
In one sentence
Open source is a culture of sharing knowledge: a program's blueprint is made public so people worldwide can improve it together, within clear rules.