Tiered link building boosts your site’s authority by using two levels of links....

https://foxtrot-wiki.win/index.php/How_Do_Tier_1_vs_Tier_2_vs_Tier_3_Links_Actually_Work%3F

Tiered link building boosts your site’s authority by using two levels of links. Tier 1 links point directly to your site and should be high quality. Tier 2 links support those Tier 1 pages, making them stronger in search rankings