Name of ForeignKey Back Relation?
In the terminology used to to talk about conceptual design of database, this is called inverse relationship. So you could say:


  master has an inverse relationship with table detail.


See for instance: Fundamentals of database systems, by R. Elmasri, S. Navathe, Addison Wesley, ISBN: 978-0-13-608620-8, Chapter 11, Object and Object Relational Databases.