Federated Security

Say there are two organizations A and B. Users in A needs to access a web service in B. How does the web service in B authenticate users in A? One way is to create user database in B. This means users in A needs to have  two credentials one for access resources in A and other for accessing resources in B.
Federated Security solves this use case where there is no need to create two credentials for a user. When a request from a user in A comes to web service in B then that user is not authenticated by B but the authentication requested is routed to A.

Read:
A Developer's Introduction To Active Directory Federation Services

Federation and Issued Tokens

Distributed cache - Microsoft AppFabric 1.1 for Windows Server

Microsoft AppFabric 1.1 for Windows Server provides distributed caching features.

http://msdn.microsoft.com/en-us/library/hh334305.aspx