A "Gateway Timeout" is an error message that occurs when a server acting as a gateway or proxy does not receive a timely response from an upstream server. This can happen when the upstream server is overloaded, down, or experiencing network issues, preventing it from processing the request in a reasonable time frame. When users encounter a Gateway Timeout error, they may see a message like "504 Gateway Timeout." This indicates that the server was unable to complete the request due to the delay. Users can try refreshing the page or checking their internet connection, but the issue often lies with the server or network rather than their device.