Error 404 is an HTTP status code that indicates the server could not find the requested resource. This error typically appears when a user tries to access a webpage or file that does not exist on the server, either because the URL was typed incorrectly, the page has been moved, or it has been deleted. A 404 error does not specify why the resource is missing, only that it cannot be found at the given address. Website owners often customize their 404 error pages to help users navigate back to working sections of the site.