How is class inheritance hierarchy being mapped by Grails mongodb plugin?

Question

We are using MongoDB plugin in Grails.

So I found this code, a domain object called Address:

public class Address extends EmbededDomain{
    static mapWith = "mongo"

    Region region;
    Zone zone;

    static mapping = {
        id generator: 'identity'
        region reference:true
        zone reference:true
    }
}

EmbededDomain is a class in src/groovy

class EmbeddedDomain {
    public EmbeddedDomain() {
        this.dateCreated = new Date()
        this.lastUpdated = new Date()
    }
}

Then I have Organization domain with relationship Organization has Address:

class Organization {
    static mapWith = "mongo"

    Address address

    static mapping = {
        id generator: 'identity'
    }
}

What does region reference:true mean?

After saving anOrganization when I enter the command show Collections in my MongoDB console I am not seeing collection with name Address? rather I am seeing collection with name EmbededDomain which contains all the Address, why is this happening EmbededDomain is just a Groovy class.