Marshmallow sandwiches are a sweet treat made by placing a layer of marshmallow between two pieces of graham crackers or cookies. They can be enjoyed as a simple snack or dessert and are often associated with outdoor activities like camping. These sandwiches can be customized with various ingredients, such as chocolate or peanut butter, to enhance their flavor. They are easy to make and can be prepared quickly, making them a popular choice for kids and adults alike.