A sandwich is not limited to a single layer of filling between two pieces of bread. It can have more than one layer of filling and bread. Each layer of filling is commonly referred to as a "deck". For instance, a single decker sandwich would be the standard two slices of bread and one layer of filling. A double decker sandwich will have three slices of bread with two layers of fillings. Generally one piece, is one piece of bread cut in two with a filling between each piece. 