open source
The practice of making software source code publicly available for anyone to read, audit, and verify. Bitcoin's open source code means no hidden backdoors are possible and anyone can confirm the rules of the system themselves.
Open source software is software whose source code is publicly available for anyone to read, inspect, modify, and distribute. In contrast to proprietary software, where the inner workings are hidden, open source makes the logic of the program fully transparent. This means that any programmer in the world can examine exactly what the software does, verify that it behaves as advertised, and check for errors or malicious code.
For Bitcoin, open source is not an optional feature — it is a foundational requirement. Bitcoin Core, the primary implementation of the Bitcoin protocol, is publicly available on GitHub and has been reviewed by thousands of developers worldwide. Because the code is open, no developer or company can quietly introduce a backdoor, inflate the supply, or alter the rules without the change being visible to everyone. The transparency of the code is what makes the system auditable and ultimately trustworthy.
Open source is also what enables trust without central authority. Users do not need to take anyone's word for how Bitcoin works. Anyone with the technical skills can verify the rules directly in the code: the 21 million cap, the halving schedule, the transaction validation logic. The code is the law in Bitcoin, and because the law is public, no one can secretly change it.