What is the difference between cost of sales and cost of goods sold?

What is the difference between cost of sales and cost of goods sold?
There is no difference between the cost of goods sold and cost of sales. Both are same.
What if Cost of Sales relates to a service rather than a "good"? Does that not signify a difference? For example a cost of sales for a service would contain no starting and finishing inventory component as is described in some texts as a way of calculating cost of goods sold.