What used to be called as Relationships in pre-10.4 versions are renamed to "Networks" in 10.4.x releases.
Also there's a new feature called "Hierarchy" introduced that is to be used for non-pictorial strict Parent-Child based relationships.
You can divide your configs among these 2 features based on the most suitable data depiction and management needs
In current releases, relationships are split in to two-- hierarchy relationship and network relationship.
So you will be viewing only the above two option on Provsioning Tool modeling layer.
Hierarchy relationship -- A connection between two business entities that is hierarchical. For example, the Organization business entity the parent of the Person business entity.
Network relationship -- A connection between two related business entities. For example, the Person business entity is related to the Credit Card business entity.
To Add on, If you already have relationships in Hierarchy Manager that you want to continue to use, you must upgrade your relationships and create them as hierarchy relationships or network relationships.
Please refer to the screenshot attached by Dhananjay for easier reference.