Question: Where is the term  "Red sauce" used?
About the article "Ketchup", section "Terminology".

Candidate passages:
The term used for the sauce varies.
"Ketchup" (sometimes spelled "catsup" in American English, called "a failed attempt at Anglicization") is the dominant term in American English and Canadian English, with "catsup" being the prominent term in some southern US states.
In these dialects, "tomato sauce" refers to pasta sauce, and is not a synonym for ketchup.
"Tomato sauce" is more common in Commonwealth English (e.g., Australia, India, New Zealand and South Africa).
In British English, the two terms are interchangeable.
"Red sauce" is used in Welsh English, Scottish English, Irish English and some parts of England, such as the Black Country, and in South London, often contrasting with brown sauce with which it is often served but in Canadian and American English, "red sauce" refers to red spicy sauces (or sweet and sour sauce) and is not a synonym for ketchup.
The etymology of the word "ketchup" is unclear, with multiple competing theories:
Nantua sauce (French: Sauce Nantua) is a classical French sauce consisting of: a Béchamel sauce base cream crayfish butter crayfish tails The term "à la Nantua" may be used in classical French cuisine to refer to any dish containing crayfish. 
Jorim is a generic Korean cuisine term referring to dishes made of vegetables, meats, seafood, or tofu in a mixed sauce by simmering for a long time.
"Jorim" is the noun of "jorida" (hangul:조리다) which means "simmering in a thick soup or sauce".
The term did not appear in cookbooks until 17th century because cuisine terms were not yet specialized in Korea.
"Siui jeonseo" is the first mentioned document on the term with a recipe for "jangjorim" (hangul:장조림).
The sauce for "jorim" is mostly "ganjang" (soy sauce) used, however, in cooking fish with red flesh such as mackerel, permit, or saury, "gochujang" or chili pepper powder is added to "ganjang" and cooked.  
Cumberland sauce is a fruit-based sauce, usually used on non-white meats such as venison, ham, and lamb.
Created sometime in the late 19th century, the sauce was named for the Duke of Cumberland, who had ties to Hanover, Germany, where the sauce was invented.
It is a more complex version of a simple redcurrant sauceDespite its German origin, today the sauce is ubiquitous in the Cumbria region of England and is thought of as a thoroughly British condiment.
Although variations exist, common ingredients include red currants or cowberries, port or wine, mustard, pepper, orange, ginger, and vinegar.  
Gravy is a traditional sauce used on roast dinner, which traditionally comprises roast potatoes, roast meat, boiled, steamed or roasted vegetables and, optionally, Yorkshire pudding, which are usually only eaten with beef.
The sole survivor of the medieval bread-thickened sauces, bread sauce is one of the oldest sauces in British cooking, flavored with spices brought in during the first returns of the spice missions across the globe and thickened with dried bread.
Apple sauce, mint sauce and horseradish sauce are also used on meat (pork, lamb and beef respectively).
Salad cream is sometimes used on salads.
Ketchup (referred to colloquially as 'tomato sauce' or 'red sauce') and brown sauce are used on fast-food type dishes.
Strong English mustard (as well as French or American mustard) are also used on various foods, as is Worcestershire sauce.
Custard is a popular dessert sauce.
Some of these sauce traditions have been exported to former colonies such as the USA.
Other popular sauces include mushroom sauce, marie rose sauce (as used in a prawn cocktail), whiskey sauce (for serving with Haggis) and cheddar sauce (as used in cauliflower or macaroni and cheese).