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

https://www.slideserve.com/richard_russell21/what-should-i-use-for-tier-1-links-if-i-want-to-rank-a-landing-page

Tiered link building uses two levels of backlinks to boost your site’s ranking. Tier 1 links point directly to your site and are high quality. Tier 2 links support those Tier 1 links, helping them gain strength and improve their value