Tiered link building helps you boost your website’s authority by building links...

https://wiki-book.win/index.php/How_Do_I_Avoid_Black-Hat_Tiered_Link_Building_Mistakes%3F

Tiered link building helps you boost your website’s authority by building links in layers. Tier 1 links point directly to your site and carry the most value. Tier 2 links support those Tier 1 links, making them stronger and more effective