noun
[mass noun]help or support
帮助；援助
no police back-up could be expected.
不能指望警方援助。
■someone or something that can be called upon if necessary; a reserve
后备人员；后备物品
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.
后备发电机。
[mass noun](Computing)the procedure for making extra copies of data in case the original is lost or damaged
(计算机)备份
■[count noun]a copy made in such a way
备份件
(N. Amer.)a queue of vehicles, especially in congested traffic
(北美)（尤指交通拥挤时）堵塞，塞车