What is "daqin"

Daqin (; alternative transliterations include Tachin, Tai-Ch'in) is the ancient Chinese name for the Roman Empire or, depending on context, the Near East, especially Syria. It literally means "Great Qin", Qin being the name of the founding dynasty of the Chinese Empire. Historian John Foster defined it as "...the Roman Empire, or rather that part of it which alone was known to the Chinese, Syria."