Body wraps were originally a treatment where Ace bandages or plastic wrap was tightly wrapped around the body to cause quick weight loss through vasodilation. You can still find these types of "slimming" body wraps, which result in the temporary loss of weight and inches, at some spas.
But today a body wrap in a spa is more likely to be treatment where you are slathered with a body mask made of algae, seaweed, mud, clay, lotion or cream, then wrapped for 20 minutes to keep you warm. Later the product is rinsed off. The body wrap usually ends with an application of lotion (technically not a massage). This body wrap treatment is sometimes called a body cocoon or body mask.