Ketchup is a condiment; in modern everyday use, the name usually means tomato ketchup. It combines tomatoes with vinegar, sugar, salt, and seasonings to make a smooth sauce with a sweet, tangy flavor.
Tomato ketchup is commonly served with fries, burgers, and other savory foods. It can also be used in glazes, dressings, and sauces. The balance of sweetness, acidity, and spices varies by brand and recipe.
Not every ketchup is tomato-based. Mushroom ketchup and other regional versions use different ingredients and may have a thinner texture or a more savory flavor.