Parfait is really a general term used to describe many different types of layered foods served in a dish. In practice, though, most Americans are familiar with ice cream or yogurt parfaits, which are a very specific type of dessert.
Also the American parfait is very similar to a sundae. It may contain layers of ice cream or cream, and include nuts, syrups, whipped cream, fresh fruit, granola, and any number of other dessert style toppings. It is a popular dessert in fairly upscale restaurants that want to offer something a bit more casual than heavier traditional French desserts. French parfait itself is traditionally made with eggs and cream whipped with a layer of fruit.