Muscovy is an alternative name for the state of Russia or principality of Moscow which is not really used anymore. The city of Moscow was originally called Moscovia as a latinized version of the cities name, but Muscovy was later applied as the name of the state itself. This name persisted in the West up into the early 18th century and can still be used in a historical context. Muscovy itself was founded in 1283 and eventually gave way to the Russian Empire in 1721 under Peter I.
In the text, the Royal Exchange, Muscovy is only referred to once. In the line “I have often been pleased to hear disputes adjusted between an inhabitant of Japan and an alderman of London, or to see a subject of the Great Mogul entering into a league with one of the Czar of Muscovy”. The speaker uses the Czar of Muscovy as an example to boast of all the amazing things he’s seen as a merchant.
Click HERE for an image of Muscovy map from 1700's