Open Source

Open-source software publishes its recipe. The code sits in public for anyone to inspect, reuse or improve, usually under a licence that says how. Linux, Firefox and most of the internet's plumbing are open source.

Most serious crypto projects are open source too, and for good reason: if you're trusting code with your money, you want people able to check it for bugs and back doors. It also means anyone can copy a project and launch a near-clone, a fork. Open code isn't the same as audited code, though; it only helps if someone actually reads it.