Dinesh,

  In a database management system (DBMS), a trigger is an SQL procedure that is executed when a record is added or deleted. It is used to maintain referential integrity in the database. A trigger may also execute a stored procedure. Triggers and stored procedures are built into DBMSs used in client/server environments.

sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedures. We can also have user defined stored procedures which can be called in similar way.