back·up/`bækˏʌp; ˈbækʌp/ n 1 [C] a copy of something that you can use if the original thing is lost or does not work 后备副本: Always make backup files at the end of the day. 每天工作结束之前都要做好备份文件。 2 [C,U] someone or something that provides help or support when it is needed 后备［支援］人员; 备用物品: Four more police cars provided backup. 另有四辆警车作支援。