A deep link is a hypertext link to a page on a website other than its homepage. Deep links are often used to link directly to products of an online store to or appropriate content. In backlink building, deep links are of particular importance in the strengthening of subpages and in long-tail optimization.
Deep links have the purpose of bringing users through to the content searched for, without having to go through the homepage and menu to find their target. At the beginning of the Internet age, when the search engine indexes were not yet as precise and the results of searches were not as accurate, deep linking was an important instrument to generate visitors and thus traffic to a website.
Today, this purpose has mostly moved to the background. Now, deep links help in search engine optimization because with it link juice can be routed directly to subpages. However, this practice should be used with caution as Google may rate deep linking as link spam or manipulation of the SERP in extreme cases and penalize the subpage in question.
Google itself uses deep links in the form of rich snippets or sitelinks. One can differentiate between deep links that direct to respective subpages or deep links that link within a document to a lower section. The aim in this example is to direct users in larger documents within Wikipedia, directly via deep link to their desired location. Deep links can be found in the SERP for Facebook page apps.
Deep links therefore primarily concern the usability of a website.
A hyperlink that points to a deeper level of a domain can also be useful for link hubs, lists of topics or in citations. Again, the user’s interest is in the foreground.
Price comparison portals also work with deep links. In this case, this type of link is necessary because the potential customer would want to find and buy the exact product he is comparing.
Deep links usually pass on link juice and PageRank. They are therefore often used by SEOs to strengthen subpages and hence long-tail optimization. What is important in this practice, however, is that the ratio between the quantity and quality of inbound links to the homepage is balanced with the strength and number of incoming links to subpages. Thus, the link profile would be conspicuous if a website has only one backlink to its homepage but several hundred deep links that direct to a particular subpage. When link building, SEOs should put due attention on the distribution of backlinks. The decisive factor is what anchor texts are used. It would, for example, be conspicuous if a deep link from a website with a lot of domain trust and high domain popularity points with a money keyword to a relatively weak subpage of a website.
However, there may be exceptions. It may be possible that a subpage gets an especially large number of backlinks as part of a marketing campaign or a provocative article in a blog has found a lot of attention and was thus often linked to. It can be assumed that search engines like Google can tell if this is an exception or deliberate, artificial linking.