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

https://wiki-aero.win/index.php/What_Should_I_Do_If_My_Tier_1_Backlink_Disappears%3F

Tiered link building helps you boost your website’s ranking by creating links at two levels. Tier 1 links point directly to your site, giving it strength. Tier 2 links support those Tier 1 links, making them more powerful