A Rice Krispie treat is a sweet dessert or snack made from Rice Krispies, melted margarine or butter and melted marshmallows. Sometimes marshmallows and/or cereal that is seasonal is used to make these treats holiday specific. They are often homemade, but one can find them in many stores usually packaged under the Rice Krispies brand.
One variation is to use chocolate instead of marshmallows which is known as "Chocolate Crackles". Kellogg's has now produced commercial varieties of both the marshmallow and chocolate-based treats under the name of "Rice Krispies Squares".
Rice Krispie treats were invented in 1928 by Mildred Day, who was at the time working for the Kellogg Company, the maker of Rice Krispies. She used the cereal to develop the snack as a fundraiser for a Camp Fire Girls group.