Offal, as Webby so obligingly points out below is "off fall". The English etymology for the word leaves little doubt as to how English speaking countries regard these extraneous parts of the animal - basically as discards. With a few notable exceptions, such as liver, brains and kidneys, people from these countries are at best hesitant, and at worst horrified by the thought of eating anything but the prime cuts of meat.
It is therefore lucky in one manner, that people from non-English speaking backgrounds were sometimes not so fortunate as the G7 nations. They often could not afford the choice cuts of meat we cherish, and were loath to let anything go to waste, more importantly, they refused to eat poorly.
In those unimaginable days, long before Red Hat linux releases, long before global economies, and long before Xbox, PS2 and Gamecube vied for our wallets, there were people much like us, sans the technology and money. They had no refrigeration, and no supermarkets. If they wanted meat, they had better damn well hoped that a neighbor had killed a beast recently.
This is the charm of offal, even if the thought of eating liver or kidneys turns you green, you really should appreciate not only the willingness of previous cultures to eat this stuff, but to prepare and eat it well, and develop cuisines that survive to this day, based on what was once so disparagingly called "off fall".
So what exactly is offal anyway? The most succinct definition is any meat that is not considered prime muscle. This includes any internal organs, as well as any extremities such as tails, feet, ears and heads. Many countries have divergent and long established cuisines based around offal, but the one constant is the treatment different parts of the beast requires. Consider this list an overview - an introduction to how these euphemistically phrased "variety meats" are cooked. Do not however, treat this list as gospel. There are many different types of offal, and many more types of preparation - search out regional recipes if you want an authoritative view on how to deal with a certain cut.
This is the stuff that you will most likely be familiar with. Even if you have never eaten it (and even if you never intend to), you can most likely find this stuff at your local butcher - even if you need to order it in advance.
The liver of pigs, sheep, cows and poultry are a common item on the dinner table - for some. This would most likely be the cut that most non-offal eaters are familiar with. Liver is not only eaten whole, but it is also often incorporated into other dishes such as pâté. If you thought that offal was poor man's fare, don't forget the extortionately priced and barbaric French delicacy, foie gras. This is artificially fattened goose liver and chefs around the world clamor to pay big dollars to get their hands on some. The Chinese revere pig's liver - along with most cuts of pork, while Anglo cooks generally choose livers from lamb or veal.
Whatever beast the liver came from, it should be cooked in one of two fashions. Either quickly, so that the liver remains a little pink in the centre, or for an extended period of time, such as in duck liver parfait.
Kidneys are generally taken from one of three beasts: cow, sheep or pig. This favourite food of Leopold Bloom gave rise to the quaint celebration of Bloomsday. Along with liver, kidneys would have to be one of the most accepted offal meats in English speaking countries.
As a blood purifier, kidneys deal with a great deal of liquid waste. This sometimes leaves kidneys smelling of - you guessed it - urine. The larger the animal, the more pungent the aroma. Generally, ox and pork kidneys have the most forthright smell. Just like liver, kidneys should be cooked either very rapidly, or slowly and for a longer period. Anything in between will result in a rubbery, inedible mess.
If ever a marketing person earned their keep, this would have to be it. Imagine the scene - "OK, we got these thymus glands, but nobody is buying them." Why not just give them two re-assuring and homely names - sweet and bread. The combined thymus and pancreas of sheep and calves are most often used, although pork sweetbreads can sometimes be found. They are usually blanched in boiling water, then the outer skin removed. After this preparation they are generally fried or grilled.
The internal mouth organ of oxen, young calves, sheep and pigs are a delicacy cooked according to the beast from which they came. Generally, the larger and older the beast, as in ox tongue, a longer cooking time is required. More tender tongues, such as from lamb, will be ready in a shorter period of time. Often the preparation of tongue will require two steps. Firstly, the tongue is simmered in a flavoursome broth. Once taken out of the liquid and cooled, the skin is removed, allowing the tongue to be sliced and cooked quickly, such as pan-frying or grilling.
Once again, another form of offal that is acceptable in many English-speaking countries. The most common type used is lamb's brains, although veal and ox brains have their adherents, such as the French. Brains need to be washed thoroughly to remove any blood and membranes surrounding the lobes. They are usually then poached, then cooled before proceeding with a recipe. Most often this will be crumbed and fried brains.
The cheek of pigs and ox are considered to be a gelatinous delicacy. Both require delicate preparation and long, slow cooking. After quite a few hours of gentle braising, cheeks end up tender, and quite sticky, due to the high gelatin content of the muscle.
The most common form of tail available is oxtail. This highly gelatinous cut is generally cooked in slowly braised dishes, reminiscent of osso buco. Oxtails need to be cut into short lengths by your butcher and tend to give off a great deal of fat while cooking. Because of this many oxtail dishes are cooked in two steps - the first cooking to make the tail tender, followed by a cooling period to let the fat rise to the surface. After skimming the fat, the tail sections are then re-heated.
Trotters and shin
Trotters refer to the feet, hooves or shanks of cows, pigs or sheep. They are generally sold on the bone and require long, slow cooking. If you have ever eaten osso buco, you have for all intents and purposes eaten trotters, as they are basically the shin of veal. (Well it’s close enough to the foot anyway).
Lamb and veal shanks are normally browned by firstly frying, then set in a flavoursome liquid to braise slowly for several hours. There is a famous Parisienne bistro dish of crumbed pig's trotters. The pork feet are first simmered in stock until tender. Once cooled, the larger bones are removed and the whole foot is coated in breadcrumbs. This is then set under an overhead grill (broiler) until crisp and served with tartare sauce, resulting in a sticky and delicious classic.
Not so common offal
This is the stuff that you will most likely never see at your local butcher. These meats are either too bizarre for western palates, or simply illegal, as bladder is in NSW.
The most important and hard-working muscle in most mammals' bodies, and therefore the toughest. Hearts of oxen, heifers, pigs, sheep and poultry can be used, and are always cooked for a fair amount of time to tenderize the tough muscles. In Europe hearts are often braised or stewed until tender, while in the carnivorous wonderland that is South America, cubes of heart are set on brochettes and grilled over coals.
The whole head of certain beasts are used in traditional European cookery, but none is prized as much as calf's head, which is prepared and served whole in classic French cuisine. The head of pork and lamb is common in rustic French country cookery such as pâté de tete and museau de porc. Ever eaten brawn? Then you have eaten head - brawn is simmered down pig's head, the meat flavoured with herbs and set in its own gelatinous aspic.
The ears of pigs and calves are considered a great delicacy in France and several other nations. They need to be singed over an open flame to remove any excess hair, soaked to removed any blood, then simmered to make them tender.
Once these steps have been followed, ears are simply fried or grilled, or perhaps coated in breadcrumbs before cooking.
Here is another one for the marketing people. Can't sell your lungs? - Why not call them lights. Yeah, that's right - the culinary term for lungs is lights. Generally calves' lungs are used. They must be beaten to expel any lingering air, and again, as with any tough muscular offal, they are cooked slowly in dishes such as civet.
The bladder itself is not eaten, but it is a vessel in which to cook other meats and poultry. Most often pigs' bladders are used and this French technique is given the phrase en vessie. There is a semi-infamous case of a young Sydney based chef that wanted to cook an arcane and intricate French dish for a food competition. The dish involved placing slices of black truffle under the skin of a hen, which was then placed in a bladder for slow baking. Could he get a pig's bladder? Not easily. In a display of bureaucratic bumbling, the young chef had to get food department clearance, then gather the bladder himself from an abattoir, while the bemused workers looked on.
Of all the inside-bits I have discussed above, this would be the one I have the least experience with. In fact, I have only ever seen it once - beef spinal cord, sold in a plastic container in Chinatown. I take it to be a Chinese delicacy, because those other culinary adventurers, the French and Italians, seem to make no mention of it. You will forgive (and possibly thank) me for not supplying a cooking method.