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

https://seo.edu.rs/blog/how-do-i-build-tier-2-content-that-looks-natural-and-not-forced-11162

Tiered link building uses two levels of backlinks to boost your site’s ranking. Tier 1 links point directly to your site from trustworthy sources. Tier 2 links support those Tier 1 links, making them stronger and safer