Off-site SEO is fixated on getting backlinks that functionally point back to a certain website to appear across the Internet. Backlinks without the "nofollow" element are among the most desirable outcomes for any website trying to appear before other websites in front of potential customers using search engines because the ranking algorithms employed by the engines consider the presence of these backlinks to be a greatly important factor. Backlinks are clearly not treated equally between the different types of websites they can appear on, however. Whether the external website is a reputable name in its respective industry or an unsavory outlet that does nothing but amass backlinks for the sake of its paying clients directly determines whether the ranking algorithms consider those backlinks "spam." Website owners and the SEO professionals who can work on their behalf can benefit from viewing the overall pool of backlinks the website may get as divisible into three "tiers" of quality and relevance. The most desirable kind of backlink can be provided by websites that are commonly seen as leading authorities in the industry in question. Search engines care about how there would be virtually no chance that these links will have been formed through "dirty" methods. In between these and the aforementioned unsavory websites, many of the backlinks that appear on web blogs and unpaid websites are considered by Google to be adequately relevant to the website they point to. These are mostly desirable so long as the websites they are posted on are not considered to have been overtaken by spam. It generally does not help a website's ranking if all of the links among all three of the "tiers" are pointing directly to it because the spam associated with the lowest tier can technically reflect poorly on it. However, a website can "filter" the quality of its backlinks by taking measures to get the mid-tier links to point to the websites providing the top-tier links instead. Likewise, the site should strive to have a large proportion of the bottom-tier links pointing to the second-tier sources instead of itself. For more information click here https://www.reddit.com/r/SEO/comments/9nq31f/whatistierlinkingin_seo/.