IEEE 802.11d is an IEEE 802.11 amendment that adds geographical regulations to the original standard. IEEE 802.11d facilitates the development of wireless local area network (WLAN) devices that comply with the wireless communications regulations of their respective countries.
IEEE 802.11d is also known as IEEE 802.11d-2001.
Techopedia explains IEEE 802.11d
IEEE 802.11d was developed out of necessity, as initially, IEEE 802.11 was limited to only a few geographical domains. IEEE 802.11d was approved to provide recommendations for wireless communications, whereby geographical information is added to transmitted frames. This specification was applied to the frame format of beacons, probes and probe requests.
IEEE 802.11d allows a device to self-configure and operate according to the regulations of its operating country and includes parameters like country name, channel quantity and maximum transmission level.