An internal link refers to a link on your site that points to another page on the same site. In practical terms, it’s what your site visitors use in order to navigate around your site, and broadly speaking it includes every link in your navigation, (both header and footer), and any links you may have in the content that point to other internal pages.
In addition to the vital service of allowing users to view the different pages of your site though, internal links perform several other functions that are less obvious, but equally important.
Flow & Structure
Your site links set out the hierarchy of your web pages, from the top level pages with broad information (or categories of product as the case may be) to the deeper pages with specific information about a single product or service.
They help to definer the paths that users will take through your site as they look for specific information, and they also create the path that search engines will follow as they index your website. As such, it’s important to plan your internal navigation carefully to make content accessible to both search engines and users.
As well as your original site map, Google also crawls the internal links in order to find content. Whenever its crawler encounters a link it follows it, and crawls the content on the page that the link points to. This means that if you plan your internal links well, you can improve the chance of a new page ranking for specific terms.
PageRank
Named for Google co-founder Larry Page, PageRank refers to the amount of authority that a page has, based on the number of other sites or pages that link to it, and although the public Google PageRank (or PR) was discontinued some years ago already, it was done in order to try and prevent site owners and SEO practitioners from focusing solely on the numbers, and internally, PR remains an important factor in Google’s algorithm.
Essentially, the way it works is that each link to a page carries a portion of the preceding page’s PageRank with it, and confers it on the target page. If, for example, you had a page with a PR of 5, and had 5 links on that page which each pointed to a different page, the links will pass a PR of 1 to each of the target pages. (If you only had to links pointing away from that page, each would pass a PR of 2.5 etc.)
This can allow you spread authority throughout the site and concentrate it on specific pages if necessary.
Over-Linking
It’s also important to keep in mind that you can quite easily have too many internal links, and if that’s the case, you run the risk of diluting your pages authority to the point where it becomes meaningless.
Things like boiler-plate footer links which are the same on every page should be no-followed to prevent them from “leaking” that PageRank to pages which do not need to be optimised, like your terms & conditions and privacy policy.
Filling every bit of content with dubiously relevant links to other internal pages will not only present Google with an unnatural internal link structure, but also cannibalise the authority that your pages already have, and that can even decrease your ranking, particularly if you’re stuffing the content with keyword rich anchor text.
Internal Linking The Right Way
The good news is that if your site has been rationally structured, and if approach the question from the point of view of the user, it’s likely that you will already be set up for a well optimised internal linking strategy.
Ask yourself, “Do I have content that would be useful for a reader to be able to find from this specific point?” and if the answer is yes, then link to it with relevant anchor text. (Anchor text should tell the user what they can expect to find if they click a link. “Click here” is bad. So is “Learn more.” But turning the relevant part of the sentence into a link to the relevant content, like this link to SEO fundamentals that will always work, is perfect.
It’s also important to make sure that relevant links are prominent. Hide the link at the bottom of the page, and the chances that somebody will click on it are much lower, and thanks to Google’s “reasonable surfer model” that link will be assigned a far lower weight than one which is in the content, prominent, and positioned where it would be logical to expect that a user would be looking for more in-depth information.
As with most SEO though, if you focus on the user, the user experience, and the information that the user needs, you’re probably off to a good start already.