Running delete_instance() method on a model instance delete corresponding row from the mapped table.

obj=User.get(User.name=="Amar")
obj.delete_instance()

On the other hand, delete() is a class method defined in model class, which generates DELETE query. Executing it effectively deletes rows from the table.

db.create_tables([User])
qry=User.delete().where (User.age==25)
qry.execute()

Concerned table in database shows effect of DELETE query as follows −

(''DELETE FROM "User" WHERE ("User"."age" = ?)'', [25])