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

https://www.4shared.com/office/BIObF2h6fa/pdf-72309-44204.html

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