Some projects are made available under multiple licenses, typically by including more than one license files, or by listing more than one license separated by commas, or with a conjunction (“and”, “or”). Examples:
MIT, BSD MIT and GPL MIT or GPL MIT, BSD and GPL
If multiple licenses are listed, it is always assumed that the user can select any of them, not that they must accept all.
There exists several versions of the GNU GPL. Each version is given a distinguishing version number. If a code library is simply licensed under (“GPL”) and does not specify a version number, you're may choose any version of the GNU GPL ever published by the Free Software Foundation. However, to use the library with Drupal, you should choose (“GNU GPL version 2 and later”.
If a code library specifies a version number of the GNU GPL License which applies to it and “any later version”, the user have the option of following the terms and conditions either of that version or of any later version of GNU GPL published by the Free Software Foundation.
For example, a code library licensed under one of the following specifications of the GNU GPL may be used in a project that is licensed under “GPL version 2 and later”, “GPL version 2”, “GPL version 3”:
GPL GNU GPL version 2 and later GNU GPL version 2 or later GNU GPL version 2 and any later version GPLv2+