What does entity Relation Model models?

What does the entity Relation Model models?

In Entity Relationship Model there exist "entities" extracted from a particular scenario. Those entities should exist in real world and can be described.
Then, second work is to define the business rules among these identified entities . Business rules can be called multiplicity. This is possible when developer should have understanding of Domain knowledge for which he/she identify relationship.
Illustration of this model is called Entity Relationship Model.