A shoe department carries more than 55 different styles of white sandals. This is the description of the Shoe Department's Merchandise Depth.
In a company, there may be different line of products, called as merchandise breadth. They may vary from each other. And within a single product line, there can be a variety within it. Like in a production factory of shoes, there are different style of shoes with different colors. So if the factory produces 55 or more pairs of different shoes in a single color, then it is said to be practicing the Merchandise Depth.