WordPress is licensed under the GPLv2 license (or later), which is an open source license. It is also a free/libre licence. The OSI is the only widely accepted

WordPress is licensed under the GPLv2 license (or later), which is an open source license. It is also a free/libre licence. The OSI is the only widely accepted authority on the definition of open source in software. You can find the open source definition (according to the OSI) here: https://opensource.org/osd https://opensource.org/osd The FSF and Richard Stallman have released their definition of free/libre software here: https://www.gnu.org/philosophy/free-sw.en.html https://www.gnu.org/philosophy/free-sw.en.html . As you can see, the definitions of open source software and free/libre software are almost identical for all intents and purposes. This was not accidental, when the OSI wrote the definition of open source, they derived it from the Debian Free Software Guidelines, which was highly influenced by the FSF's Free Software Definition. They wanted to rebrand free/libre software, which keeping the same criteria. All open source licences are also free/libre licences, and all free/libre licences are also open source licences. The difference between open source and free/libre lies in the differences between the philosophies that the FSF and the OSI promote. The FSF say that using any licences other than free/libre is unethical, whereas the OSI does not comment on using software that is not open source. It's a matter of branding and of connotations.