MVCC

from The Free On-line Dictionary of Computing (8 July 2008)

Multi-Version Concurrency Control
MVCC

   <database> (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)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

MVCC
       MultiVersion Concurrency Control [system] (PostgeSQL, DB)