Error 404, also known as the “Page Not Found” error, is a common HTTP status code that appears when a web server is unable to locate the requested webpage. This error occurs when a user attempts to access a webpage that no longer exists, has been moved, or has been deleted. It can also occur when there is a mistake in the URL or when the server is experiencing technical difficulties. The number 404 is derived from the 4xx series of HTTP status codes, which indicate client-side errors. This error can be frustrating for users, but it serves as a helpful reminder to double-check the URL and ensure that the webpage is still available.