triggers are special type of stored procedure which are 
automatically invoked at the time of modifyibg tables

Trigger is the collection of T-SQL statements, which is 
activated based on certain actions. Trigger is fired, when 
any of one DML statements will occur..

Triggers are basically used to implement business rules. 
Triggers is also similar to stored procedures.
The difference is that it can be activated when data is 
added or edited or deleted from a table in a database.

Trigger gets executed when an INSERT UPDATE or DELETE occurs

2 types of triggers are INSTEAD OF triggers and AFTER triggers

Triggers are a special type of Stored procedure which
execute automatically when a triggering action like INSERT,
UPDATE or DELETE occurs.

INSTEAD OF trigger
- executes automatically in place of triggering actions like
INSERT, UPDATE or DELETE
- executes before PK, FK constrains are checked

AFTER trigger
- executes automatically after the statement that triggered
it completes
- executes after constrains are checked

Trigger is a special type of store procedure.when we are going  
to insert,update,delete table automatically trigger is invoked