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

https://www.bust-bookmark.win/tiered-link-building-organizes-your-backlinks-into-layers-to-boost-seo-more-1

Tiered link building uses two levels of backlinks to boost your site's ranking. Tier 1 links point directly to your site from quality sources. Tier 2 links support those Tier 1 sites, helping improve their authority