Implicit Transactions
When a connection is operating in implicit transaction mode, 
Microsoft® SQL Server™ automatically starts a new transaction 
after the current transaction is committed or rolled back. 
You do nothing to delineate the start of a transaction; 
you only commit or roll back each transaction. Implicit 
transaction mode generates a continuous chain of transactions.

After implicit transaction mode has been set on for a connection,
 SQL Server automatically starts a transaction when it first 
executes any of these statements:

ALTER       TABLE           INSERT
CREATE    OPEN             DELETE
REVOKE    DROP             SELECT
FETCH      TRUNCATE   TABLE
GRANT     UPDATE 


The transaction remains in effect until you issue 
a COMMIT or ROLLBACK statement. After the first 
transaction is committed or rolled back, SQL Server 
automatically starts a new transaction the 
next time any of these statements are executed by 
the connection. SQL Server keeps generating 
a chain of implicit transactions until implicit transaction 
mode is turned off.

Implicit transaction mode is set either using 
the Transact-SQL SET statement, or through 
database API functions and methods.