The relationship between two or more distinct elements (Entities) in a System. For example, one could say that a particular job Function is carried out according to a specific Procedure. Therefore Function and Procedure have a defined relationship.
Well... they may have a relationship. Whether it is or should be 'defined' is another question. Is it not odd that an EntityModel should 'be' a relationship? A relationship implies two or more entities (in an EntityRelationshipModel, that is). So an EntityModel may be:A representation of two or more entities and the relationships between them. The entities will typically have unique names and the relationships will typically have defined for them, as a minimum, optionality and cardinality.