Okay kiddo, so have you ever been to a really big store before? One that has lots and lots of different things to buy, like toys, clothes, electronics, and even food? That's what a department store is!
It's kind of like a bunch of smaller stores all in one big building. Each "department" is a section of the store where they sell certain things. For example, the toy department will have lots of toys and games, while the clothing department will have lots of different clothes to choose from.
A department store is a great place to go when you need to buy lots of different things, because you can find everything in one place! Plus, they often have sales and discounts to help you save money.