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Product Item
A product item is a specific type of product that is provided by the company. An example of a product item of Adidas is a pair of running shoes.
Product Line
A product line is a variety of products that are differentiated by features such as colours, functions, sizes and so on. An example of a product line of Adidas is their shoes as under that category they have running shoes, basketball shoes, football shoes, tennis shoes and so on. And these are different because of their functions, sizes and colours.
Product Mix
A product mix is a variety of product lines that the company owns. In Adidas' case, an example of a product mix would include footwear, apparel, accessories and so on.
Product Range
A product range is the combination of a product line and product mix.