Open source

Open Source means that the "source code", the language programmers use to make computers do their jobs is avalible to everyone. The opposite is closed source, where the programmer hides the code. Open Source has been around for decades, but it became popular with Linux and BSD software communities. Anyone can change the code and see how it works. To protect the code, a special liecense is used. The most common kinds of licence is the GPL, BSD and LGPL. Wikipedia uses open source too.