According to the search results, "tossing salad" is a slang term that refers to the act of performing anilingus on someone, which involves stimulating the anal opening and the surrounding area with ones mouth. The term originated in prison slang, where lower inmates were forced to lick the anuses of leading inmates, but they put salad dressing on it to hide the taste. However, this origin story is not confirmed and may not be true. It is not related to the culinary term "tossing salad," which refers to mixing salad ingredients and dressing.