In SQL Server 6.5, this command specifies that a distributed transaction managed by Microsoft Distributed Transaction Coordinator (MS DTC) starts and the transaction_name specifies a user-defined transaction name that is used to track the distributed transaction within MS DTC utilities:
BEGIN DISTRIBUTED TRANsaction [transaction_name]
You should use the BEGIN DISTRIBUTED TRANsaction statement instead of the BEGIN TRANsaction statement when a transaction is to be processed on one or more remote servers. The command alerts MS DTC to manage the transaction processing on the local and remote servers.