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

https://www.first-bookmarkings.win/tiered-link-building-uses-two-levels-of-links-to-boost-your-site-s-seo-tier-1

Tiered link building uses two levels of links to boost your site’s rankings. Tier 1 links point directly to your site, while Tier 2 links support those Tier 1 links