N on Nostr: what is tracking token?

{ "id": "6b1eda5597ee7e671d3608c78482c72daf40ca916f8591ebde04a00b47de0581", "pubkey": "cf44ec8d43ca813823e986bb66147c7aeba5787db1946a07975a3b6f7b346a7b", "created_at": 1720804440, "kind": 1, "tags": [ [ "p", "cf44ec8d43ca813823e986bb66147c7aeba5787db1946a07975a3b6f7b346a7b" ], [ "p", "c558c7cc69bbda3c271782b736babc64acd2da258b14f356dbca966cb0b7b89e" ], [ "e", "5c866f8aca28f343af177fe00deb95a8d727735d6d369fa7c0b2072fca4df877", "wss://relay.primal.net", "root" ], [ "e", "c569b9eab2c655b0b25c7280cacc99010e3c1cb69aa5616f4e3543d689922ef4", "wss://ftp.halifax.rwth-aachen.de/nostr", "reply" ] ], "content": "what is tracking token?\n", "sig": "5fd1316e9d1678275f3ee8b9837c9004acfdd82cc173d4a11ad53dda1350ef2ecbd637256c0b751bbcc1b5128b124a091d353dbc044b48e93a9db8f2228d421c" }