Store - Order Problem Lets there are n stores.

A customer order x items. All the stores might not have all the items from the order.

So find the store/combination of stores that can serve the order request such that the combination that contain least number of stores.

Edit: 

Example: Lets say there are 4 stores. User is ordering item 1, 3, 6, 7

Store 1 sells item 1, item 6
Store 2 sells item 1, item 2, item 3, item 4, item 5
Store 3 sells item 6, 7, 8, 9, 10
Store 4 sells item 5, item 7

The combinations of stores that can fulfil the orders
{ 2, 3 } , { 1, 2, 4}

So optimal solution in this case is {2,3}

P.S: I was asked this question in an interview. What would be the algorithm that would fit into the problem?
Your problem is essentially the same as set cover, a classical NP-complete problem.

In set cover, we are given sets $S_1,\ldots,S_n$ together covering a universe $U$, and the problem is to find the smallest subset that still covers $U$. The only difference between this and your problem is that you want to cover some $V \subseteq U$. You can get the classic formulation by intersecting all sets with $V$.