Full Orders Only?

What do they mean by "full orders only"?

That you must have all the items a customer, or group of customers, have ordered.
If they want two burgers, a coke, and a coffee, you cannot bring them two burgers and a coke in one trip and the coffee in another trip.
You can, however, have more items than they ordered. If someone wants an expresso and an ice cream, and someone else wants an expresso and a burger, you could grab both expressos while you were at the machine. Then you could get the ice cream, burger, or both and deliver them.