This is a read-only text field, up to 64 characters, recorded in the call history table showing the session target of the peer that was used for a now-completed call leg via the telephony interface. An admin uses this historical record to confirm after the fact which configured session target actually handled a specific finished call, useful when investigating routing behavior retroactively. For example, an admin investigating why a completed call ended up somewhere unexpected could check this history field to see exactly which session target was in effect for that call at the time.