Can someone explain what a relying party trust is. I am configuring IFD for CRM but I cannot find basic information on what a relying party is and what is does?
The way I would describe this is that CRM is the relying party, it is relying on ADFS to check the claims that are made ("I claim that I am userX"). In ADFS you configure a relying party trust to tell ADFS where it can expect claims to come from - it will trust the relying party so that when a user is authenticated they can be redirected back to that application (you don't want to give a user a token to present to an application you do not trust).