Error 503 is an HTTP status code that indicates a server is temporarily unable to handle a request. This can happen for various reasons, such as server overload, maintenance, or issues with the server's resources. When users encounter this error, they typically see a message stating that the service is unavailable. This error is part of the HTTP protocol, which is used for communication between web browsers and servers. A 503 error is usually a temporary issue, and users may be able to access the website again after some time or when the server is back online.