Understanding Exchange Server 2007 server roles
Exchange 2007 introduces a new Exchange term: “Server Role”. Server role is a logical concept used to organize Exchange 2007 services and features across one or more servers. While Exchange 2003 provided primitive server roles called BackEnd server and FrontEnd server, Exchange 2007 has more granular divisions.
Read at source: http://msexchangeteam.com/archive/2006/09/12/428880.aspx
