Why was the empire called Ottoman? When did the Byzantine Empire cease to exist?

1) Why was the empire called Ottoman? 2) When did the Byzantine Empire cease to exist? 3) what were the feudal relations in the Ottoman Empire? 4) What are the main events in the national liberation movement of peoples? 5) What is the Turkish epic?

Because initially the founder of the dynasty, which after several centuries became for a time the strongest power in the world, was a khan named Osman. His beylik was originally located in the northwest of Asia Minor. And he himself was one of the descendants of the generals of the Seljuk Turks, who received a land allotment for his service. The Ottoman Empire was not immediately called Ottoman. It became an empire (or sultanate in the Muslim world) in 1453 with the capture of Constantinople, the fall of Byzantium and the renaming of the city to Istanbul.