Answer: Indirect Lookup relationship
Explanation:
Indirect lookup relationship is used when there is no Salesforce ID in the external data. So this relationship basically links the external object which is the 'child' to the custom object which is the 'parent'.
As the question states, universal containers has included its orders as an 'external data object' into salesforce. Now it wants to create a link or relationship between accounts and orders objects. This is possible through indirect lookup relationship.