Clarification in Licensing Language
WordPress has always stated that its license was the GNU GPL, and has bundled version 2 of the license, even though no GPL version was specified. The text of version 2 (as well as 1 and 3) says that if no version is specified, the software can be redistributed under the terms of any version of the GPL published by the FSF.
However, WordPress contains libraries which are licensed under the GPL “version 2 or any later version,” which obviously excludes version 1 of the GPL. Here is the reality: the GPL version 1 is effectively irrelevant. It hasn’t been a commonly used license since before Matt Mullenweg was in third grade! Clarifying WordPress as being licensed under the GPL “version 2 or later” resolves these niggling library licensing concerns or ambiguities, and clarifies where WordPress stands.
It was the intention of the WordPress founders and developers to be GPL version 2 or later from the beginning, and we have now made that license properly explicit.