Source : Free On-Line Dictionary of Computing

Multi-Version Concurrency Control
     
         (MVCC) An advanced technique for improving
        multi-user {database} performance.
     
        The main difference between multiversion and lock models is
        that in MVCC locks acquired for querying (reading) data don't
        conflict with locks acquired for writing data and so reading
        never blocks writing and writing never blocks reading.
     
        This technique is used in the {free software} database
        {PostgreSQL}.
     
        (1999-06-18)