In the broadest meaning of "medicine", there are many different specialties. In the UK, most specialities have their own body or college, which have its own entrance examination. These are collectively known as the Royal Colleges, although not all currently use the term "Royal".
The development of a speciality is often driven by new technology (such as the development of effective anaesthetics) or ways of working (such as emergency departments); the new specialty leads to the formation a unifying body of doctors and the prestige of administering their own examination.