Tier 1 links are your direct authority boosters while Tier 2 links help them...

https://golf-wiki.win/index.php/How_to_Build_Links_Slowly_So_Google_Does_Not_Freak_Out

Tier 1 links are your direct authority boosters while Tier 2 links help them stay relevant. Using Ahrefs to monitor your backlink profile helps you see how these layers push rankings up without overdoing it