why is linux referred to as open source software?
 Linux is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. The development of Linux is one of the most prominent examples of free and open-source software collaboration. The underlying source code may be used, modified and distributed‍—‌commercially or non-commercially‍—‌by anyone under the terms of its respective licenses, such as the GNU General Public License. 