Source : Free On-Line Dictionary of Computing

two-phase commit
     
         A technique for maintaining {integrity} in
        distributed {databases}.  Where a system uses two or more
        database, a transaction among the distibuted database should
        be {atomic} ("all or nothing").  This is done by handling the
        transaction in two phases.  First the databases prepare the
        transaction, confirm that it is possible to process it, and
        lock the relevant record.
     
        Once all the required databases confirm that the transaction
        is viable, the system instructs them all to {commit} it -
        i.e. to make it permanent.  If it is not possible to process
        it, the system will instruct the databases to {rollback}
        (undo) the transaction.
     
        (2000-02-28)