404 Server Code
The 404 or Not Found error message is a standard response code indicating that the client was able to communicate with a given server, but the server could not find what was requested. Having these on your site, generally as a result of broken links, sends negative feedback to Google, as it appears that the site is not well-maintained, and they should be fixed by removing the offending link or redirecting that URL to a working page. Removing and fixing these is critical to technical SEO services.