Braising combines two cooking methods. Usually first pan searing or surface browning in some fat, followed by a long slow cooking in a small amount of liquid, which deepens the aroma. Braising meat that have tough parts in them, called collagen, gradually converts the toughness in a wonderful smooth gelatine. This conversion happens at temperatures above 70 C. The tough cuts are slow cooked for a long period. So that the food can be cut by a fork. It is fine for the meat to also contain some fat.
A typical braise takes place with the whole food submersed for 2/3 in the cooking fluid. But also braising whole birds or game such as chicken, duck or rabbit all benefit from this cooking method.
The braising liquid will become more flavorful during the slow cook. May be later it served as the base of a sauce or a gravy.
Even vegetables can be braised in their own juices.
Boeuf Bourguignon, Osso Bucco, lamb stew, cock au vin, Chinese braised chicken pot, Chinese pork knuckle and just preparing a whole duck or a rabbit all benefit from a slow cook. But also cooking spinach and endives in their own juices are examples.