A product line is a group of related productsmanufactured by a single company. For example, a cosmetic company's makeup product line might include foundation, powder, blush, eyeliner, eye shadow, and lipstick products that are all closely related. The same company might also offer more than one product line. The cosmetic company might have a special product line geared toward teenagers and another line geared toward women older than 60, in addition to its regular product line that can be used by women of any age.

Source: investopedia.com