Rurt is an onomatopoeiac term for ketchup/sauce as it resembles the sound made when the condiment is squirted/extracted from its container.
The word Rurt originates from the Newtownards area of Northern Ireland and its best pronunced with your finest insult-tinged Northern Irish accent.
Ketchup = Red Rurt, HP Sauce = Brown Rurt, Mayo = White Rurt, Mustard = Yellow Rurt, Humous = Greek Rurt, Salsa = Spanish Rurt etc...