A shopping cart is software installed on your web hosting account, along with or in place of your website, that allows the creation of an online store where products can be purchased. If you've ever ordered anything online, chances are you've already used one.
Shopping carts give you the tools to develop a product catalog with pictures and prices, as well as manage your inventory, shipping costs and order fulfillment. Most importantly, your shopping cart allows you to take credit card payments on your website when connected to a Payment Gateway like PayJunction.
There are many varieties of shopping carts to choose from, each with different strengths and weaknesses. Some carts are entirely free while others charge a monthly fee. Your web developer can help you select from the list of compatible Shopping Cart Systems based on your particular business needs.