The term Royal House refers to the official designation and name of a royal family instead of surname.
Reigning European Sovereign Houses
Deposed Sovereign Houses
In these countries there are now republics.
Other Reigning Sovereign Houses
Most Royal Families do not have surnames: those that have adopted them rarely use them. They are referred to instead by their titles, often related to an area ruled or once ruled by that family. The name of the Royal House is not a surname, just a way of identifying individuals.
The example where a Royal House has adopted a surname is the United Kingdom. Britain's Royal House is the House of Windsor. However, following a decision by Queen Elizabeth II, descendants of Her Majesty and her husband, Prince Philip, Duke of Edinburgh, have a different surname to that of the Royal House. It combines the surnames of both of their parents, namely Mountbatten-Windsor. Similarly, though the British Royal House name under Queen Victoria and King Edward VII was Saxe-Coburg-Gotha, the personal surname of Victoria's descendants was Wettin. In 1917, both the Royal House name and surname were changed to Windsor.