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

https://www.mediafire.com/file/nrp96eu65bubrdm/pdf-35636-18300.pdf/file

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