Source code is the foundational component or source information of a computer program. It is written as human-readable plain text in a programming language comprised of a set of instructions used to produce various outputs. Source code enables computer programmers to specify exactly what actions should be performed by a computer. The source code will typically be transformed by another piece of software, called a compiler or interpreter, from the source language into the programming language, in order to create an executable program. The translated code is called object code.
The source code for a computer program is usually stored in text files on the computer’s hard disk, or it can be stored in a database.
Legal protection for the creators of source code has had an interesting history. Before 1974 source code was not copyrightable in the United States, and was always in the public domain. It became copyrightable in 1974, and in 1983 the protections were extended to cover object code as well. Owners/vendors of proprietary software rely on copyright protections to maintain exclusive rights to distribute and modify the source code of their programs. Because of that, proprietary software is often referred to as closed-source software. By contrast, open source software is free to use, distribute and modify, and these freedoms are protected by innovative software licenses like the GNU General Public License (GPL).