Tiered link building uses two levels of links to boost your site’s authority....

https://touch-wiki.win/index.php/How_Do_I_Pick_High-Quality_Sites_for_Tier_1_Backlinks%3F

Tiered link building uses two levels of links to boost your site’s authority. Tier 1 links point directly to your pages and carry the most weight. Tier 2 links support your Tier 1 links, making them stronger and more effective