A user whose account resides in an account partner organization and who can access federated applications that reside in a resource partner organization. In the context of Office 365, a federated user is one that is sourced (mastered, authenticated, created, and managed) in an organization’s on-premises Active Directory. The onpremises Active Directory has a trust relationship with the cloud that allows authenticated Active Directory users to access cloud resources (or -€œservices,-€? such a SharePoint Online, Exchange Online, etc).
An external user who has valid credentials from a federated partner, which is a trusted outside organization that is enabled for access to your Lync Server or Office Communications Server deployment.