Which of the following does "federation" most likely refer to within the context of identity...

Facilitating groups of users in a similar function or profile to system access that requires elevated or conditional access

An authentication mechanism that allows a user to utilize one set of credentials to access multiple domains

Utilizing a combination of what you know, who you are, and what you have to grant authentication to a user

Correlating one's identity with the attributes and associated applications the user has access to