The Error 404 or Page not found occurs when a website visitor asks for a page that cannot be found on your site. This error page is displayed, which is a HTTP (Hypertext Transfer Protocol) standard response code, and indicates that the request for the page was communicated and received by the server but the server was unable to find it. The usual reasons for the display of the Error 404 are incorrect links on the site or the requested page may have been moved or deleted. A 404 Error page also indicates that the page that was requested may be available again in the future. The 404 error page should not be confused with the "Server Not Found" error page which means that a connection to the server did not occur at all.

Customize your error page
In general, a web server will issue a HTML page with the 404 code and the "Not Found" phrase by default. However, one can configure a web server to display a customized error page, with a better and more informative description, the site's logo or branding and perhaps even a search form. It is highly recommended that you customize your error page for the following reasons: the standard error page doesn't let your visitor know why they were shown the error page; it doesn't have the same consistent look or match the other pages of your site; and it doesn't assist the visitor in any way leaving them feeling lost. A custom error page lets visitors to your site know that you care and that you have made an attempt to help and guide them through the dead end they have encountered.

A good error page should have the following:

• an error message that is written in plain, non-technical, apologetic language that users will easily comprehend
• should tell the visitor what went wrong
• should provide link options to other pages on the site
• has a link to the webmaster or a form to submit broken links, and a search field linked to the site's search engine and a list of links close to what was entered
• no advertisement displayed
• it avoids redirection of 301 and 302

Track and Prevent 404 Errors
Log Files: The majority of HTTP errors are recorded in the transfer log and error log files. By observing these files, you will get an idea of the occurrence of 404 errors, how frequently they happen, consistencies, and the actual document that was the cause of the error. From these log files you can also find out about any broken links and the misspelled URL that led to the error. Armed with all this information, you can easily correct broken links and prevent 404 errors on your website.

Redirects: If you have a web page that is constantly getting a 404 error, you can create a redirect page that will take the visitor from the old page to its new replacement page.

Robots File: If there is an area on your website that you are changing regularly, it is a good idea to block the search engines from indexing those sections by using robots.txt file so 404 errors can be prevented.