From Envirowiki

Envirowiki uses the "GFDL". The choice is an ethical one, based on the principle of copy-left - that which is freely available for use within the community, benefits the community. It also has practical benefits: content can be shared between sites like Anarchopedia, Appropedia, GreenLivingpedia, SourceWatch and Wikipedia.

[edit] 1 License specifics

The full text of the GFDL is available at www.gnu.org/licenses/fdl.html

The GFDL license that envirowiki uses means that anyone can use any of the site's content for any purpose, as long as they follow these regulations:

• Attribution
  The user must acknowledge the authors of the material (in this case, envirowiki contributors). This can be done by linking to the page in question, as envirowiki keeps track of every edit. This serves to promote the work being done by the envirowiki community, with the intention of expanding the community, and making envirowiki bigger and better.
• Share Alike
  Any derivation of the content of envirowiki also has to be shared under the same license (GFDL 1.2 or later). At some point in the future, GFDL may become compatible with other similar licenses. This maximises creative input into the global information commons, meaning it's easier for people to learn and create. And yes, it's viral. That's a good thing.

[edit] 2 Legality

This is a legal license for use of copyright. All copyright stays with the originator, you are able to use it under the terms above. Any changes you make are copyright to you, unchanged portions remain with the originator.

Content uploads to envirowiki are assumed to be released under the above license as a bare minimum, however, users may offer their work under other licenses as well, such as commercial-ok, attribution only, or public domain. This applies only to edits and additions made by that user. Users generally specify their licenses on their user pages.