Entity relationships are the representation of relations between various Dynamics CRM entities. The customization tools included with Dynamics CRM make it easy for system customizers to create new entities, modify existing entities, and create the relationships between them.
The entity relationships define associations from one entity to other entities or to itself. A new relationship is represented as a new table relationship in the database.
The simplest example of an entity relationship is the creation of a lookup to an entity. This creates a one-to-many relationship between the two entities. This allows you to associate multiple child records to a parent record.
Within Dynamics CRM, there are three types of relationships. They are as follows:
One-to-Many
Many-to-One
Many-to-Many