The classic French definition of Rémoulade Sauce is mayonnaise with the following (chopped) ingredients stirred in: capers, chervil, gherkin, parsley, tarragon, and spring onion. It’s then flavoured with some anchovy extract, and used to accompany cold meat and seafood.
There are many variations on this classic definition in the English-speaking world which swap mustard for the anchovy, and add chopped cooked egg.
A pinkish-orange Cajun version is designed to accompany mostly seafood, though occasionally it’s been spotted accompanying cajun chicken dishes. Simple renditions of the Cajun version use cayenne pepper, garlic, green onions, horseradish, ketchup, mayonnaise, olive oil, paprika, and tarragon vinegar. More elaborate versions add finely chopped hard-boiled egg, mustard, tabasco sauce and Worcestershire sauce.