In marketing jargon, product lining refers to the offering of several related products for individual sale. Unlike product bundling, where several products are combined into one group, which is then offered for sale as a units, product lining involves offering the products for sale separately. A line can comprise related products of various sizes, types, colors, qualities, or prices. Line depth refers to the number of subcategories under a category. Line consistency refers to how closely related the products that make up the line are. Line vulnerability refers to the percentage of sales or profits that are derived from only a few products in the line.

In comparison to product bundling, which is a strategy of offering more than one product for promotion as one combined item to create differentiation and greater value, product lining consists of selling different related products individually. The products in the product line can come in various sizes, colours, qualities or prices. For instance, the variety of coffees that are offered at a café is one of its product lines and it could consist of flat white, cappuccinos, short black, lattes, mochas, etc. Alternatively, product line of juices and pastries can also be found at a café. The benefits from having a successful product line is the brand identification from customers which result in customer loyalty and multiple purchases. It increases the likelihood of customers purchasing new products from the company that have just been added into the product line due to the previous satisfying purchases.