Open-Source Software - (Open System, Open Systems-based) - The open-source software's source code is made openly available (unlike Windows.) This means that programmers who want to change and hopefully improve the code, can do so, but there's a catch; they have to disclose all improvements and under most licenses, disburse them for free. At the heart of the movement may be an open-source operating system called Linux, a version of the UNIX operating system that was developed (primarily) by the Finnish programmer Linus Torvalds.