The term 'Lunchroom Stack' refers to a stack of trays used in a school cafeteria. The five-letter solution for this term is 'TRAYS'. These trays are typically made of plastic or metal and are used to hold food items such as sandwiches, salads, and desserts. They are also used to transport food from the kitchen to the lunchroom. The trays are usually stacked on top of each other in order to save space and make it easier to move them around.