One product is priced low, just to cover the costs with little or no profit margin while the other product is priced high with a very high profit margin. Both the products are complementary products i.e use of one product is complemented by the other. This strategy is basically followed to overcome the loss due to product’s sale by the profit provided by the sales of the other complementary product.
For example Printer & cartridge. This strategy is successful because once you have bought a printer; you are required to buy the complementary cartridge unless you are willing to buy in a new printer itself. Also, Companies avoid competitors selling ink for their printers by having unique cartridges.