This gives the name of the tunnel that is currently active within the encap tunnel group referenced by the notification, mirroring the active index field but in human-readable form. It lets an admin immediately recognize, for example, that 'ENCAP-PATH-B' rather than the usual 'ENCAP-PATH-A' is now carrying traffic without cross-referencing an index-to-name table. This is the kind of detail that shows up directly in an alert email so on-call staff don't need console access just to know which path is live.