Historians gave it the name, specifically it was Baron Ferdinand von Richthofen who did so in 1877. He was "a prominent geographer who worked in China from 1868-72 surveying coal deposits and ports, and then wrote a five-volume atlas that used the term for the first time." The Silk Road was not actually a single route, but rather is a term used by historians to refer to the many possible routes taken from China to the Mediterranean, sometimes including sea routes.

The quote is from Valerie Hansen, The Silk Road: A New History (Oxford: Oxford University Press, 2012) pp. 6-7.