Tiered link building uses two levels of backlinks to boost your site's ranking....

https://wiki-nest.win/index.php/What%E2%80%99s_a_Good_Tier_1_Link:_Guest_Post_vs_Niche_Edit_vs_PR_Mention%3F

Tiered link building uses two levels of backlinks to boost your site's ranking. Tier 1 links point directly to your site from quality sources. Tier 2 links support those Tier 1 sites, helping improve their authority