Yam was an interconnected route system in order to deliver intelligence and information for travelers and messengers whether it be during warfare or during political negotiation and communication.
The Yam operated with a chain of relay stations at certain distances to each other, usually around 140 miles or 200 kilometers. Messengers for example would go to the next relay station and give the information to the second messenger and rest and let the second messenger go to the third relay station to hand the document to the third messenger. This way information or documents were constantly on the move without each messenger getting tired. In each relay station there would be spare horses, food, and shelter.
The name Yam was adopted in most western languages from Russian, where it probably is a Tatar (turkic) loan word. The turkic word root again is related to the Mongolian "Zam" (road or way). However, in the Mongolian Empire, both the postal system and the individual stations were named "Örtöö" ("Örtege" in Classical Mongolian).