The restaurant term “drop on top” is an instruction given to waiters or food runners taking food from the kitchen pass to a table in the dining room. “Drop on top” means that the item or items they are running are to be added to the food that is already at the table. “Drop on top” items can be “for the table”, or shared among all the diners or they can be assigned to an individual diner. For example if a diner says to a server “can I get an order of fries with this burger” when receiving his food, the directive to the food runner from the kitchen when the fries are up will be “position 3 fries, drop on top.” Drop on top can also be referred to as "drop dirty".
Another common case for drop on top items is with free items sent from the kitchen, otherwise known as an SFN or “something for nothing”. During appetizers maybe the chef wants to send out a new menu item for this table of regulars. The new menu item is sent as SFN, drop on top.
Chef handing plates to a food runner: “Table 31, fries and Brussels Sprouts are for the table, drop on top”
Food runner: “Table 31 Fries, Brussels shared, drop on top, 31 out.”