Red cocktail onions, also known as pickled pearl onions, are small, round onions that have been pickled in a vinegar-based brine. The pickling process adds tanginess and a hint of acidity to the onions, making them a popular addition to various dishes and cocktails. Red cocktail onions are commonly used as a garnish in martinis and other cocktails, where they add a pop of color and a tangy, pickled flavor. They can also be used in salads, antipasto platters, charcuterie boards, and as a condiment in sandwiches and burgers.