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

https://www.mediafire.com/file/z9mgvqdwwo1eb8a/pdf-42897-77316.pdf/file

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