Deep Link Ratio: This term refers to the ratio of links that point to internal pages on a website compared to the overall number of links to an entire website.
A high deep link ratio generally indicates that a webmaster has built up a legitimate natural link profile. This goes for both measuring the number of deep links on his or her own website and the number of links from others. This number can often be found using the "link:" function on a Google search, but there are other platforms that track deep links, too.
When measuring this ratio, it only applies to links that direct to a specific page. It doesn't measure the amount of links to the homepage. The ratio is derived from the number of deep links divided by the number of links overall. For instance, a total of 50 deep links divided by 100 links total would be a ratio of 50% -- a fairly high number in most cases. There isn't necessarily a magic number in terms of what makes a good ratio.
Webmasters looking to increase deep link ratios on their sites can do so by adding additional content and promoting that content accordingly. Linking from page to page on an individual website can help to keep users on the site and increase the amount of click throughs one receives.