Relations are associations between one model and another in the domain and in the database.
Embedded relations describe documents who are stored inside other documents in the database. Embedded relations are associations between one or many objects where the child object is embedded within the parent in the same document in the database
Referenced relations describe documents that reference documents in another collection by storing data (usually an id) about the other document in itself. In other word Referenced relations are associations between documents that reside in separate collections.