An open sandwich, also known as an open face sandwich or open faced sandwich, consists of one slice of bread with one or more food items on top of it. Technically a half bagel with a topping is an open sandwich.
It is the common, traditional sandwich type in the Scandinavian countries, where it is typically eaten at lunch, but may also be eaten as part of breakfast and/or supper. It is also available in Vienna, as well as other parts of Europe, for lunch.
The Scandinavian smørrebrød / smørbrød / smörgås consists of one piece of buttered bread, often rugbrød — a hard, whole-grain rye bread, topped with any of a variety of meats, including various cold cuts, bacon, herring, fish fillets, eggs and leverpostej (liver paté), and then usually some vegetable (for example, thinly sliced cucumber, tomato wedges or pickled beets) and then usually a condiment, such as mayonnaise, or toasted onion bits. A traditional replacement for butter on a piece of bread with herring is pig fat. There are many traditional variations associated with the smörgås / smørbrød / smørrebrød. There are special stores which specialize in these sandwiches.
The Dutch and Flemish Uitsmijter arrives on a large plate with 2 large slices of usually white bread, and a selection of meats, cheeses, vegetables and possibly an egg arranged between. The dish is often served as a hearty breakfast.
Legally, In the United States the ruling in the case of Panera Bread Co. v. Qdoba Mexican Grill established that a true sandwich (from a legal perspective) must include at least two slices of bread. An open-faced sandwich does not satisfy this condition.