名詞 backup:

1. an accumulation caused by clogging or a stoppage
2. someone who takes the place of another (as when things get dangerous or difficult)
   同義詞：stand-in, substitute, relief, reliever, backup man, fill-in
3. a subordinate musical part; provides background for more important parts
   同義詞：accompaniment, musical accompaniment, support
4. (computer science) a copy of a file or directory on a separate storage device
   同義詞：computer backup
5. the act of providing approval and support
   同義詞：backing, championship, patronage

back.up

n.（名詞）

A reserve or substitute.
改變或替代
Computer Science A copy of a program or file that is stored separately from the original.
【計(jì)算機(jī)科學(xué)】 備份：從原文中獨(dú)立出來單獨(dú)貯存的程序或文件的副本

Support or backing.
支援或支持
Music A background accompaniment, as for a performer.
【音樂】 伴奏：為一個(gè)演奏者配音伴奏
An overflow or accumulation caused by clogging or by a stoppage:
阻塞：由阻礙或停頓引起的泛濫或堆積：
例句：
a backup in the sink; a backup of traffic at the drawbridge.
下水道堵塞；吊橋上的交通阻塞

adj.（形容詞）
Extra; standby:
額外的；替補(bǔ)的：
例句：
a backup pilot.
候補(bǔ)飛行員