Pentaho supports both Enterprise and Community editions. The community edition is free and usually has fewer features than their Enterprise releases, but they are the same in the application core.
The enterprise version of BI Server, that is, Business Intelligence, has recently been renamed BA Server - for Business Analytics. The community version still uses the BI server name.
The Pentaho website has a feature matrix that displays the differences: http://www.pentaho.com/explore/packages/ . However, this matrix is much less useful than the one that was published in the past. You may need to dig further.