Custom Relationships
Custom relationships are the reusable relationships defined in the meta model. They define relationships between a business model object and another business model object, a business model object and an imported model object, or an imported model object and another imported model object. For example, the custom relationship "Is Defined By" defines a relationship between an imported model object and a term.
When used in the WHERE clause, the filters with the custom relationship can be used with the =, !=, =ANY, !=ANY, !=ALL, !=ALL, =WHERE, !=WHERE, EXISTS and NOT EXISTS operators.