mall指的是步行街商场,是一个概念；department store是指百货商店
department store [countable]
a large shop that is divided into separate departments, each selling a different type of good
一个大的商店，分成不同的区域卖不同的东西
mall [countable] especially American English
a large area where there are a lot of shops, usually a covered area where cars are not allowed [= shopping centre]
一片儿由多个商店组成的区域
mall
1 An urban shopping area limited to pedestrians.
步行街：只限于步行者通行的城市购物区
2 A shopping center with stores and businesses facing a system of enclosed walkways for pedestrians.
大型步行区购物中心：通对一个封闭的只对步行者开放的人行道的购物中心，有各种商店和商行
department store
A large retail store offering a variety of merchandise and services and organized in separate departments.
百货商店：一种大型零售商店，它提供各式各样的商品和服务，并分成各个独立的部门