What are triggers in PostgreSQL?

A trigger is a function that is automatically called when a specified event (INSERT, UPDATE, DELETE, TRUNCATE) occurs on a table or view. Triggers are created in two steps: (1) create the trigger function that returns TRIGGER: uses NEW (new row data) and OLD (old row data). (2) attach it with CREATE TRIGGER. Timing: BEFORE (can modify NEW), AFTER (sees committed data), INSTEAD OF (for views). Level: FOR EACH ROW or FOR EACH STATEMENT. Example: auto-update updated_at: create a function that sets NEW.updated_at = NOW() and attach as BEFORE UPDATE trigger. Triggers enable audit logging, enforcing complex constraints, and maintaining derived data.