What is the difference between identity linking and identity mapping?

Identity linking is a definition-time act that connects two digital identities from different domains and stores the link; identity mapping is the runtime act of resolving such links, so that a local digital identity is connected to the federated one presented at login.

* Linking stores the connection once; mapping resolves it on every login. *

A linking protocol is the protocol used to establish the link. Think "link once, map on every login".

Go deeper:

• Social login (Wikipedia) — identity linking in its most common everyday form.