I'm not sure what you want to know about apple and banana coulis, as coulis means a thick sauce. The definition is as follows:

"A French culinary term which has undergone some changes in its career. In old English cookbooks, the word cullis is found, but this has fallen into disuse and coulis has taken its place. At one time, coulis were sauces and also the juices which flowed from roasting meat. Some cooks called liquid purees coulis, but only those prepared with chicken, game, fish, crustaceans, and some vegetables. Today, coulis donotes some thick soups made with crayfish, lobster, prawns, and other crustaceans, the word being employed where bisque has formerly been used."