In a website, an external link will send you to a page that is in another domain - eg. if you click an external link from www. yahoo. com it will send you outside of www. yahoo. com.
Internal links are links that go from one page on a domain to a different page on the same domain.
External Links are hyperlinks that point at target any domain.
To explain in simpler terms: An internal link is a link which, when clicked, will take the user to a different page but on the same website. An external link is a link which, when clicked, will take the user to a different page but the page is also on a different website (i.e. an external link takes the user to a different website, an internal link doesn't). I hope that helps.
Internal linking is the hyperlink that target to the same domain whereas External linking is the link that link off your website to somewhere else over the internet.
An internal link is one that goes to other areas within your site.
An external link is one that goes to another URL outside of your site, or links from other sites to yours.