A French word, that translates to "outside the work." the restaurant service staff used to prepare these small bits of food for guests to enjoy while the kitchen staff prepared the hot meal.
Technically, appetizers are served as the first course (introduction to a meal), while hors d'oeuvres are served to whet an appetite (before the meal).
Canapés: Mini, open-faced sandwiches. Typically, they are constructed from a base (bread, cucumber, endive, mussel, etc.), a spread (flavored butter, cream cheese, etc.) and garnishes.
Crudités: A raw or slightly blanched vegetable served as an hors d'oeuvre. Some commonly used vegetables include broccoli, carrots, celery, cauliflower, and radishes.
Caviar: The salted roe (eggs) of the sturgeon fish. Often considered a very premium hors d'oeuvre, the most common types include beluga (most expensive), osetra, sevruga, and pressed.
Sushi & Sashimi: Sushi is raw or cooked fish/shellfish rolled on seasoned rice. Sashimi is raw fish eaten without rice. And just so you know, in Japan, sushi (zushi) refers only to the flavored rice.
Small Skewers (brochettes): Meat, poultry, game, fish, shellfish or veggies on a skewer. Typically they are marinated, then baked, grilled, or broiled, and served with a side sauce for dipping.
Filled Dough: This category encompasses phyllo dough, savory pie crust, or puff pastry dough. Typically they are stuffed with a variety of fillings, both meat and veggie based.