A tomato-based condiment with a tang contributed by vinegar, sugar, salt and spices. Ketchup is said to have originated with ke-tsiap, a spicy pickled-fish condiment popular in 17th century China. British sailors brought ke-tsiap home; and throughout the years it included anything from nuts to mushrooms. It wasn't until the late 1700s that New Englanders added tomatoes to the blend and it became what we know as ketchup.
1 cup tomato sauce + 1/2 cup sugar + 2 tbsp vinegar = 1 cup ketchup