In DBMS, a trigger is a set of procedural statements that are automatically executed in response to certain events on a particular table or view in a database. Triggers are used to maintain the integrity of the data by changing the data of the database in a systematic fashion. They are a special kind of stored procedure that is activated in response to a particular event in a database. Triggers can be invoked when a row is inserted into a specified table or when specific table columns are updated. They can be used to enforce business rules, maintain data integrity, and automate certain actions within a database.

Triggers are defined using SQL statements and are associated with a specific table. They can be triggered by various events, such as inserting, updating, or deleting data in a table, and they allow you to perform additional operations based on those events. There are different types of triggers, including DML triggers, DDL triggers, and logon triggers.

The syntax for creating a trigger in SQL involves defining the name of the trigger, the event that triggers the trigger, the table on which the trigger is to occur, and the trigger body. Triggers can help enforce data integrity, validate data before it is inserted or updated, keep a log of records, and improve the performance of SQL queries. However, they may also increase the overhead of the database and be difficult to troubleshoot.