A royal waiting room is a space at a train station set up for use by a royal family when they travel by train. According to protocol, a monarch never has to wait. So when they arrive somewhere, everything is already ready. However, this is not feasible when traveling by train. Stations are needed for regular train services and it is therefore not possible for royal trains to be placed along platforms for a royal family in advance. That is why some stations are equipped with a waiting room with some comfort and sufficient privacy. These waiting rooms are often found in stations near royal palaces.
Since royal persons started traveling by train in the second half of the 19th century, both royal private railroad cars and waiting rooms became available for them. When representative new stations were built near a palace during this period, royal waiting rooms were often built within them.