Interesting attempt on the 
definition of social CRM (and the evolution to get to it) by Oliver Blanchard at the BrandBuilder Blog:
[Social] CRM is a business function supported by a system and technologies whose aims are to improve a company’s ability to derive insights into customer needs and behaviors by adding to their transaction data the lifestyle data they share online.
From my perspective it covers well the aspect of adding the outside social information to the existing inside view of CRM.
However, In the age of Facebook, Twitter, Youtube and all other social media, I think there is also the aspect of adding the social network capabilities to the CRM part, i.e. let your followers and friends do part of your customer relationship, especially the promotion and brand building part of it. Some others would probably also call it Word-of-Mouth-Marketing.
This obviously also depends on what should be considered under CRM and then you can think about externalizing some of the functions. For me key business functions of CRM are Customer Care, Complaint Management, Bonus and Loyalty Programs, Promotional Campaign Management and there is probably an official definition somewhere.
And to add to this ReadWriteEnterprise just summarized the latest from Gartner on Social CRM.