Bidirectional association allows us to fetch details of dependent object from both side. In such case, we have the reference of two classes in each other.
Let's take an example of Employee and Address, if Employee class has-a reference of Address and Address has a reference of Employee. Additionally, you have applied one-to-one or one-to-many relationship for the classes in mapping file as well, it is known as bidirectional association.
Visit our one-to-one and one-to-many mapping pages to learn about it.