back-up
/ˈbækʌp/noun
1
- mass noun help or support帮助; 援助：
no police back-up could be expected.
不能指望警方援助。
1.1
- someone or something that can be called upon if necessary; a reserve后备人员; 备用物品：
I've got a security force as back-up
我有一支保安队作为后备力量
as modifier a back-up generator.备用发电机。
2
- mass noun Computing the procedure for making extra copies of data in case the original is lost or damaged【计算机】备份。
2.1
- count noun a copy made in such a way备份件, 副本。
3
- N. Amer. a queue of vehicles, especially in congested traffic〈北美〉（尤指交通拥挤时的）堵塞, 塞车。