In contrast to an external link which originates from a different website, an internal link both originates from and points to a location within the same website.
Internal linking is very important to search engine optimization because of the way in which it affects both the end-user experience and the ability of the search engine bot to penetrate a website to access all of its public web content.
One of the objectives of comprehensive search engine optimization is to ensure that each internal link is part of a well-defined, strategically planned linking structure that is easy to follow by both end-users and search engine bots. Each internal link is grouped and named to demonstrate to both end-users and the search engines the type of web content the link points to. An accurately named link is as important as a Title Tag because both work to identify the nature of the content to be found on the corresponding web page.
Websites that have poorly designed and inaccurately named internal links suffer from more than bad usability issues. A search engine bot penetrates a website by following links. Depending on how the link path is designed, it is actually possible for the bot to get caught in a sort of eddy, travelling round and round from link to link without ever having the ability to access and scan the web page content. Obviously if the search bot can’t scan your content it is not going to be indexed and your web pages will not appear in the search engine results pages.
It is critically important to search engine optimize your internal links to ensure the best possible end-user experience and the ability of the search engines to find, access and scan your web page content so that it can be accurately indexed.