Although the definition of an external link may vary from site to site or from person to person. An external link is often described as any link that goes to a different domain. For example, example.com and someplace.com are considered external links to computerhope.com.
How is an external link different than an internal link?
An internal link only links to pages in the same domain or subdomain; an external link can link to any domain. For example, both of the links in this paragraph link to internal links on the Computer Hope domain.
Many sites (including Computer Hope) differentiate external links from internal links to help visitors know they'd leave the site if they visited the link. For example, on Computer Hope, we use a small box with an arrow (e.g., visit google), a common symbol that indicates you'll leave the site if the link is visited.
Other examples of external links
Other situations can also cause a link to be thought of as internal instead. For example, if a site has subdomains or directories that host different sites on that domain (e.g., a site that hosts numerous blogs or homepages, or business sites). For example, the site someplace.com could have different blog subdomains like cooking.someplace.com, autorepair.someplace.com, etc. Although all these sites are internal to the site, some services may consider them external links.