Master Data Management (MDM) comprises a set of processes and tools that consistently defines and manages the non-transactional data entities of an organization (also called reference data). MDM has the objective of providing processes for collecting, aggregating, matching, consolidating, quality-assuring, persisting and distributing such data throughout an organization to ensure consistency and control in the ongoing maintenance and application use of this information. (Source: Wikipedia MDM)
Appararently MDM will be part of the SharePoint vNext platform if you look at the new MDM section on Microsoft.com - http://www.microsoft.com/sharepoint/mdm/default.mspx. If you want to know where all this is heading, take a look at the Microsoft's MDM Roadmap.
It is quite strange though - if you look at Kirk Haseldens blog post - Surprise! MDM Technology Preview available tomorrow (dated November 2007) - it states that a CTP should be available somewhere in Q3 2008 - but the last few months - no more news about it.