Suet

Suet is the raw, hard fat of beef, lamb or mutton found around the loins and kidneys.
Suet has a melting point of between 45 and 50 °C (113 and 122 °F) and congelation between 37 and 40 °C (99 and 104 °F). Its high smoke point makes it ideal for deep frying and pastry production.
The primary use of suet is in tallow, although it is also used as an ingredient in cooking, especially in traditional baked puddings, such as British Christmas pudding. Suet is rendered into tallow by melting and extended simmering, followed by straining, then cooling. The process may be repeated to refine the product.
The word suet /ˈs(j)uːɪt/ is derived from Anglo-Norman siuet, suet, from Old French sieu, seu, from Latin sēbum ('tallow', 'grease', 'hard animal fat'). Sebum is from the Proto-Indo-European root *seyb- ('pour out, trickle'), so it shares a root with sap and soap.
As suet is the fat from around the kidneys, the connective tissue, blood and other non-fat content must be removed. It must be refrigerated prior to use and used within a few days of purchase, similar to raw meat.
Pastry made from suet is soft in contrast to the crispness of shortcrust pastry, which makes it ideal for certain sweet and savoury dishes.
Suet is found in several traditional British dishes, such as the sweet baked puddings jam roly-poly and spotted dick. Savoury dishes include dumplings, which are made using a mixture of suet, flour and water rolled into balls that are added to stews during the final twenty minutes or so of cooking. In the savoury dish steak and kidney pudding, a bowl is lined with a suet pastry, the meat is placed inside and a lid of suet pastry tightly seals the meat. The pudding is then steamed for approximately four hours before serving. Suet is also an ingredient of traditional mincemeat, which is also referred to as 'fruit mince'.
Due to its high energy content, cold weather explorers use suet to supplement the high daily energy requirement needed to travel in such climates. Typically the energy requirement is around 5,000–6,000 Cal per day for sledge hauling or dog-sled travelling. Suet is added to food rations to increase the fat content and help meet this high energy requirement.
Cakes of suet are popularly used for feeding wild birds and may be made with other solid fats, such as lard. Rolled oats, bird seed, cornmeal, raisins, and unsalted nuts are often incorporated into the suet cakes.
Pre-packaged suet sold in supermarkets is dehydrated suet. It is mixed with flour to make it stable at room temperature, requiring some care when using it for recipes calling for fresh suet, as the proportions of flour to fat can change. Most modern processed recipes stipulate packaged suet.
Also available is vegetable suet, which is made from refined vegetable oil.
Consumption of suet is forbidden according to Jewish law and it was reserved for ritual altar sacrifices. This restriction only applies to those animals which were used for sacrifices, and thus does not include wild animals such as deer. Maimonides in his book Guide To The Perplexed, writes that one of the ideas behind this commandment is that the Torah wants to teach people to develop the discipline to avoid very tasty foods that are unhealthy.