Least Expensive is where you purchase 'x' amount of items then get a percentage discount on the lowest priced item. 


For example the promotion may be "Buy 3 and get the least expensive for half price".


You should create an Item Bundle with the item(s) that are included in this promotion.


In the first field you enter the number of items from the Item Bundle the customer must purchase i.e. 3


In the second field you enter the percentage discount the customer receives i.e. 50%


In the third field you enter the number of items the promotion applies to i.e. 1


Click the Save button when done.