Tsargrad was not used as a name of the city, but as a nickname manifesting the regal dignity of the city. At the same time the historic Slavonic names of the city were Константинь градъ (in Old Church Slavonic as well as Church Slavonic) and Константиноградъ (only in Church Slavonic). Both are direct translation of the Greek name of the city (Κωνσταντινούπολη) and mean the city of Constantine.
Tsargrad is an Old Church Slavonic translation of the Greek Βασιλὶς Πόλις. Combining the Slavonic words tsar for "Caesar" and grad for "city", it stood for "the City of the Caesar". Per Thomsen, the Old Russian form influenced an Old Norse appellation of Constantinople, Miklagard (Мikligarðr).
Bulgarians also applied the word to Turnovgrad, one of the capitals of the Bulgarian tsars, but after the Balkans fell under Ottoman rule, the Bulgarian word has been used exclusively as another name of Constantinople. In the vernacular of the Bulgarian Slavs the Ottoman sultans were called tsars.
After the fall of Constantinople in 1453, the burgeoning Russian Empire had begun to see itself as the last extension of the Roman Empire, and the force that would resurrect the lost leviathan (Third Rome). This belief was the supported by the Russian Orthodox Church and given at least an air of legitimacy by the marriage of Ivan III to the heiress of the last Byzantine Emperor. It was allegedly an objective of the Tsars to recapture the city, but despite many southern advances and expansion by the empire, this was never realized owing to the Western interference in the Crimean War.
As the zeitgeist which spawned the term has faded, the word Tsargrad is now an archaic term in Russian. It is however still used occasionally in Bulgarian. A major traffic artery in Bulgaria's capital Sofia carries the name "Tsarigradsko chaussée" ("Road to Tsarigrad"); the road continues into the main highway to Istanbul.