Relevant section From Wikipedia:
>Academia.edu is not a university or institution for higher learning and so under current standards it would not qualify for the ".edu" top-level domain. However, since the domain name "Academia.edu" was registered in 1999, before the regulations required .edu domain names to be held solely by accredited post-secondary institutions in the US, it is allowed to remain active and operational. All .edu domain names registered before 2001 were grandfathered in, even if not an accredited USA post-secondary institution.