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

https://delta-wiki.win/index.php/What%E2%80%99s_the_Safest_Way_to_Build_Links_Over_Time_Without_a_Penalty%3F

Tiered link building uses two levels of backlinks to boost your site’s ranking. Tier 1 links point directly to your main site, giving it strong, direct value. Tier 2 links support those Tier 1 links, making them stronger and more effective