What is the difference between SCM and SVN? And how does git differ from mercurial?
SCM generally means Software Configuration Management, which include CMRM (Change Management up to Release Management), including versioning.
SVN is only a VCS: Version Control Tool.
So one is much more complete and covers more completely the development lifecycle, while being generic: Team Fundation Server or RTC - Rational Team Concert - are both examples of SCM.