There's an ongoing debate not only about enterprise 2.0 definition on wikipedia but also on whether such a definition has to exist or not.
There's what it seems to me being the "original" definition by A. McAfee :"enterprise 2.0 is an enterprise that uses blogs and wikis". AlthoughI consider this definition is too restrictive because it doesn't embrace the full range of enterprise, it's, at least, a good and common starting point (my definition's here).
Wikipedia choosed to redirect E2.0 definition to "enterprise social software". It's even worst than McAfee original...