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

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

Tiered link building uses two levels of links to boost your site’s authority. Tier 1 links point directly to your site and carry the most value. Tier 2 links support those Tier 1 links, making them stronger and more effective