An internal link is a hyperlink that allows navigation from one page in a website to another.
Although mostly used for navigational purposes in a website, internal links helps the readers in accessing more information via related articles or pages.
Internal links not only play an important part in navigation inside website, but also help in increasing page views and internal page rank.
Techopedia explains Internal Link
Advantages of using internal links in a domain:
User friendly and easier for navigation: Proper placing of internal links allows readers easy navigation through the website. It also helps them in finding relevant content and articles.
Increase of pageviews and reduction of bounce rate: By placing relevant internal links, readers spend longer amounts of time on the website navigating through the different pages created. This in turn increases the pageviews. One of the biggest advantages of internal links is the dramatic reduction of the website's bounce rate.
Improved indexing and crawling of the website: Search engines would find it easier to crawl and index the website based on the internal links. Indexing becomes more convenient by use of internal links.
Increase in PageRank: High quality backlinks placed in one page of website will act as backlink for other pages in same site if internal links are well established.This in turn would help in increasing the pagerank for the website.
Improvement in search engine rankings: With improvement in page rank, the backlinks and the internal links help in improving a website's search engine rankings.