Proper noun
GFDL
Initialism of GNU Free Documentation License.
Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. Source: Internet
Some of these (such as Enciclopedia Libre) use GFDL or compatible licenses as used by Wikipedia, leading to exchange of material with their respective language Wikipedias. Source: Internet
Free downloadable PDF with open-source GFDL license. Source: Internet
Note that it was possible only because 1) CC-BY-SA and GFDL are both copyleft and similarly restrictive, 2) FSF released a new version of the license on purpose! Source: Internet