A galley is a kitchen on a cruise ship (or any vessel, for that matter). Most cruise ships will have one large galley, located by the main dining room, where the majority of food prep is done, plus additional, smaller galleys to serve specialty restaurants and the buffet. In a cruise ship galley, health and safety are key; countertops and appliances are stainless steel, and there are no open flames, as fire is especially dangerous on a ship. Everything is organized, with designated prep and storage spaces for specific types of food and often a separate space for preparing foods for special diets. You'll find an army of crew members there at all hours, making dough and baking bread, churning their own ice cream, prepping plates in advance, cooking meat to order during busy mealtimes and washing dishes post-service.
Some cruise lines hold free or extra-fee behind-the-scenes tours that visit the ship's galley so you can learn more about food prep onboard. Some Chef's Table dinners also include a galley tour as part of the evening's events.