From eduGAIN Wiki
eduGAIN is a service that interconnects the participating identity federations. They agree on a set of common standards and policies which ensure interoperability. eduGAIN is therefore also called an interfederation service. Its goal is to enable Pan-European Web Single Sign On (Web SSO) for members of the research and education community.
The eduGAIN interfederation service is intended to enable the trustworthy exchange of information related to identity, authentication and authorisation between the member federations. The eduGAIN service delivers this through co-ordinating elements of the federations' technical infrastructure and a policy framework controlling the exchange of this information.
More overview information can be found on www.edugain.org.