[] () a copy of a file, program, etc. that can be used if the original is lost or damaged（文件、程序等的）备份◆Always make a backup of your work.你的工作文件要经常进行备份。◆a backup copy备份文件extra help, ideas, equipment, etc. that you can use if the first fails增援；替代设备◆We have a backup plan if the merger falls through.如果合并落空，我们还有后备计划。➡back sb/sth up at back verb