Ham comes from the hind leg of a pig, and if it's called ham, it usually means it's cured (though you do occasionally see "fresh hams," which are the same cut, but uncured).
There are two basic methods for curing ham: dry curing—which produces "country hams," as well as the renowned prosciutto di Parma from Italy and jamon serrano from Spain—and wet curing, which produces the "city ham" that graces countless Easter buffets and is familiar to deli shoppers.
Feeding a crowd? A half ham will serve up to 14 people; for even more guests, choose a whole ham.
If you're buying a city ham to serve a crowd (for instance, for an Easter or Christmas buffet), there are a few choices to make. There are four different grades of city ham:
Ham This highest grade of ham has a clean, delicate pork flavor and a fine, lean texture that resembles that of a chop. It's considerably more expensive than other grades, though, and your local supermarket may not carry it.
Ham in natural juices The "natural juices" are actually added water (many hams of this grade weigh up to 10% more than their raw weight due to the extra water). These hams have a fine, meaty quality when baked, and the added water does help ensure that they stay juicy. This grade is a good value and is readily available at most supermarkets.
Ham, water added The percentage of added water in this grade will be stated on the label (usually in fine print). A ham that says "water added—15%" means it weighs 15% more than its raw weight.
Ham and water product Most producers of this lowest grade pump as much water as they can into the ham, which adds weight and allows them to sell it at a lower price. If the amount of water exceeds 50%, the ham must be labeled "water and ham product," since there is more water by weight than meat.
Of these grades, your best bet is to go with either ham or ham with natural juices. Both grades are available either bone-in or boneless. Whenever you're cooking a whole or half ham, choose the bone-in version, since meat cooked on the bone will generally have better flavor.
Finally, if you're serving a half ham, you have the choice of the shank (lower) half or the butt (upper) half. The butt tends to be very flavorful and tender but it contains part of the hip bone, which can make for awkward carving. The shank, meanwhile, is easier to carve, but it's tougher and chewier.