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

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

Tiered link building uses two levels of backlinks to boost your site's authority. Tier 1 links point directly to your site, giving it real value. Tier 2 links support those Tier 1 links, making them stronger and more effective