The message with code 404 and the word Error means that the required page is not found on the website. The fact that the link indicating it is incorrect can be the cause of emergence of such page or this page was recently deleted from the website.
Depending on the browser and settings of the website, page 404 Error can look differently. Error is translated from English as "error". 404 means an error code. There are also other options of writing of this message: Error 404, 404 Not Found, Error 404 Not Found, 404 Page Not Found. Messages about this error can appear in any browser and in any operating system.
As the required page does not exist, the server gives the report that it cannot be found. The majority of such pages appear in a browser tab as any other web page.
Why page 404 Error so looks
When you visit the web page, your computer requests information from the server through the HTTP protocol. Still before the requested page appears in the browser, the Web server sends the heading HTTP containing the status code. The status code contains information on the status of request. The normal web page receives the status code at number 200. But the Internet user does not see this code because the server unloads the required web page at once. Only if there is an error, page 404 Error appears.
Why page 404 Error so is called
In 1992 the Consortium of the World wide web approved the status codes HTTP. These codes were formulated by Tim Berners-Li, the inventor of the Internet and the first browser, in 1990.
In number 404 the first digit 4 belongs to the client's error. The server indicates that the client incorrectly specified the link to the page or requested more unavailable page. 0 means a syntax error. The last digit 4 means a specific error from packet of error beginning with 40.
If the page is deleted forever, then the status code should be 410. But this code meets in practice very seldom. Much more often users see the page with code 404.
Reasons of emergence of page 404 Error
Technically emergence of page 404 Error is the client's error. The user or incorrectly specified the link, or requested already nonexistent page, but had to know that it is absent.
In certain cases webmasters delete the page from the website, without redirecting from it on other, new page. In that case also the error message 404 appears.
Sometimes the error message is loaded also for other reasons when the page actually exists and is not deleted. In that case it is possible to key F5 or to try to refresh the page. Also will help if you clean a cache of the browser and cookies.