Most software you use keeps its inner workings secret. You can use Microsoft Word, but Microsoft won't show you the actual code that makes it work — just like a restaurant might let you eat the food without sharing the recipe. Open source software does the opposite: it publishes the recipe for anyone to read, copy, modify, or improve.
What "source code" means
Every piece of software is built from source code — the instructions, written in a programming language, that tell a computer what to do. When software is "closed source" (also called proprietary), only the company that made it can see that code. When it's "open source," the code is publicly available for anyone to examine.
A closed-source app is like a vending machine: you put in money, something comes out, but you have no idea what's happening inside. Open source is like a recipe book: you can see exactly what went into the dish, change the seasoning if you want, and share your improved version with everyone else.
Who makes open source software?
Open source projects are often built by communities of volunteer programmers from around the world. Anyone can contribute — fix a bug, add a feature, improve the documentation. Popular projects might have thousands of contributors who have never met in person. They collaborate through websites like GitHub, where code changes can be proposed, reviewed, and either accepted or rejected.
Big companies also contribute to open source. Google, Meta, Microsoft, and many others have released large projects as open source, partly to attract talented developers and partly to build an ecosystem around their technologies.
Famous examples
You interact with open source software constantly without realising it:
- Linux — the operating system that powers most of the world's web servers, Android phones, and supercomputers
- Firefox — the web browser
- Wikipedia — not software, but built on open source principles
- The software running most of the internet's infrastructure
Why does it matter?
Open source software means anyone can check for security flaws (or fix them). It means software doesn't disappear when the company behind it closes down. And it means developers in poorer countries can build on the same tools as developers in Silicon Valley, without paying expensive licences. It's one of the genuine success stories of collaboration over competition.
Most software you use keeps its inner workings secret. You can use Microsoft Word, but Microsoft won't show you the code that makes it work. It's like a restaurant letting you eat the food but never sharing the recipe. Open source software does the opposite. It shares the recipe so anyone can read it, copy it, change it, or make it better.
What "source code" means
Every piece of software is built from source code. Source code is a set of instructions written in a special computer language. These instructions tell the computer what to do. When software is "closed source," only the company that made it can see the code. Another word for closed source is proprietary. When software is "open source," anyone can look at the code.
Think of it like this. A closed source app is like a vending machine. You put in your money and something comes out. But you cannot see what is happening inside. Open source is like a recipe book. You can see every ingredient and every step. You can change the recipe if you want. You can share your improved version with everyone else.
Who makes open source software?
Open source software is often built by groups of volunteer programmers. These programmers live all around the world. Anyone can join in and help. You could fix a bug, like correcting a spelling mistake in homework. You could add a new feature, or improve the instructions. Some popular projects have thousands of helpers who have never met each other. They work together using websites like GitHub. On GitHub, someone can suggest a change to the code. Other people then check the change. They decide whether to accept it or say no.
Big companies help too. Google, Meta, and Microsoft have all shared large projects as open source. This helps them find skilled programmers. It also encourages other people to build things using their tools.
Famous examples
You probably use open source software without even knowing it. Here are some famous examples.
Linux is an operating system. It runs most of the world's web servers, Android phones, and supercomputers. An operating system is like the head teacher of a computer. It keeps everything running smoothly.
Firefox is a web browser. You can use it to look at websites.
Wikipedia is not software itself. But it is built using open source ideas. Anyone can read it, and many people help to improve it.
Most of the hidden software that keeps the internet working is open source too.
Why does it matter?
Open source software lets anyone check for security problems. It also means anyone can fix those problems. If the company behind a piece of software closes down, the software does not simply vanish. Other people can carry on looking after it. It also means programmers in poorer countries can use the exact same tools as programmers in rich places like Silicon Valley. They do not have to pay expensive fees. Open source is a brilliant example of people working together instead of competing against each other.