The "HTTP 503 Service Unavailable" status code indicates that a web server is temporarily unable to handle a request. This can occur due to server overload, maintenance, or other issues that prevent it from processing requests at that moment. It signals to users that the service is currently unavailable but may be restored shortly. When users encounter a 503 error, they may see a message stating that the server is busy or undergoing maintenance. This response is part of the HTTP protocol, which helps communicate the status of web services. Typically, users are encouraged to try again later.