Tartar sauce is a condiment made of mayonnaise, chopped pickles and relish caper and herbs such as tarragon and dill. Tartar sauce can also be enhanced with the addition of other varieties of herbs, lemon juice, or olives. It is most often served with seafood dishes such as fish and chips, fish sandwiches, fish fingers, fried oysters, and calamari. Tartar sauce is based on either mayonnaise or aioli, with certain other ingredients added. In the UK, recipes typically add to the base capers, gherkins, lemon juice, and dill. US recipes may include chopped dill pickles, onions (or chives), and fresh parsley.

Source: Wikipedia