ADD is the Airport Code of Addis Ababa in Ethiopia.
"ADD" in the context of travel typically also stands for "Additional." It is used to indicate that something extra is being added to a reservation or booking. For example, an "ADD room" or "ADD night" would indicate that an additional room or night is being added to a hotel reservation. In the context of transportation, "ADD stop" or "ADD destination" would indicate that an additional stop or destination is being added to a trip itinerary.