There are about 900 breeds of sheep in the world.
Judges are generally certified to judge one or several breeds, usually in the same group, but a few "all-breed" judges have the training and experience to judge large numbers of breeds.
A specialty show may be regional or national. A "Best in Show" win at a national specialty show is tremendously prestigious, indicating that the winning dog or bitch triumphed at a contest which attracted entries from the most serious fanciers of that breed in the country or continent. Some specialty shows attract international entries.