Entity relationships are the object equivalents of the table relationship. They allow you to traverse the relationships between the tables as object links.
So, if you have a PERSON_TABLE that contains foreign keys to an ADDRESS_TABLE you need to be able to figure out which Person
EJB corresponds to which Address EJB. That's what entity relationships give you.
They allow you to say myPerson.getAddress() and get back the right Address Entity bean corresponding to the right person.
Kyle