What does an HTTP 404 error indicate?

An HTTP 404 error indicates that the resource or file you requested from the server does not exist. This status code is part of the HTTP response standard used to communicate the outcome of a request made by a client (like a web browser) to a server. When a web server receives a request for a webpage or file that it cannot find at the specified URL, it responds with a 404 status code, informing the client that the requested resource is not available. This lets the user know that the address entered may be incorrect, or that the content has been moved or deleted.

Understanding this error is crucial in web development and site maintenance because it directly impacts user experience; encountering a 404 error can be frustrating for users as it implies they cannot access the information they were seeking. It's also a common scenario that developers need to address, either by ensuring that links are correct or by providing helpful custom 404 pages that guide users to other parts of the site.