SOS
noun [ S ] uk/ˌes.əʊˈes/ us/ˌes.oʊˈes/
求助;（尤指）紧急呼救（信号）
a request for help, especially because of danger
Within an hour of the ship transmitting an SOS (message/call), six boats had arrived and started a rescue operation. 这艘船发出紧急呼救信号后不到1个小时，就有6艘船到达现场实施救援。
The hospital sent out an SOS for extra blood supplies. 这家医院发出紧急求助信息，希望获得额外的血液供应。