Okay kiddo, let me explain what an order unit is. Imagine you want to buy some apples from a store. When you go to the store, the store might sell apples in packs or boxes. The pack or box is called an order unit.
So, an order unit is the amount or quantity of a product that a retailer sells in one single package. For example, a store may sell a pack of 6 apples as one order unit. If you want to buy apples from that store, you have to buy them in packs of 6.
Sometimes, the retailer will have different order units for different products. For instance, they might sell a bag of 24 candy bars as an order unit, but a pack of 3 toothbrushes as another order unit.
In summary, an order unit is how many of a particular product you have to buy in one package or box. It's just like buying a pack of gum, a box of cereal, or a bag of chips.