Beef suet is the hard, white fat that surrounds the kidneys and loins of cattle, valued as a cooking fat for its high melting point and neutral flavor.
Suet is often confused with tallow: suet is the raw fat itself, while tallow is what you get after rendering it, melting and straining out impurities to produce a shelf-stable cooking fat.
Suet is a defining ingredient in British dishes such as steak and kidney pudding, mincemeat pies, and Christmas pudding, and its solid texture also suits steaming, boiling, and baking. In sweet applications it pairs well with dried fruit, nuts, and spices like cinnamon and nutmeg; in savory dishes it complements hearty meats, root vegetables, and herbs.