1. Plugins must be compatible with the GNU General Public License v2, or any later version.
Though any GPL-compatible license is acceptable, using the same license as WordPress — “GPLv2 or later” — is recommended. All code, data, and images — anything stored in the directory — must comply with the GPLv2, regardless of their creator. Included third-party libraries must also be compatible. For a specific list of compatible licenses, please read the GPL-Compatible license list on gnu.org. Double check all licensing as only the original owners have the authority to change them.