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

https://www.tumblr.com/powerfullyskeletaltrail/823653992075755520/whats-the-difference-between-tiered-link-building

Tiered link building uses two levels of links to boost your site’s rankings. Tier 1 links point directly to your site and are high-quality. Tier 2 links support those Tier 1 links, giving them more strength