What is "fry sauce"

n. (context US English) A condiment for french fries, usually one part ketchup to two parts mayonnaise.

Fry sauce, also commonly known as "salsa rosada" or "mayo-ketchup", is a condiment served worldwide, often with French fries and tostones. It is usually a combination of one part ketchup and two parts mayonnaise. It is similar to — but thicker and smoother than — traditional Russian dressing and Thousand Island dressing.