Hu 胡 was a general term for non-Chinese peoples living north and northwest of China. It was used mainly between the Warring States 戰國 (5th cent.-221 BCE) and the Southern and Northern Dynasties period 南北朝 (300~600). The mighty steppe federation of the Xiongnu 匈奴 was also often referred to as Hu. Peoples living east of the Xiongnu were called Donghu 東胡 "Eastern Hu". These were in first instance the Wuhuan 烏桓 and Xianbei 鮮卑. The peoples living in the many citystates of the Tarim Basin were called Xihu 西胡 "Western Hu".
The Eastern Hu, the Linhu 林胡 "Forest Hu" and the Luofan 樓煩 were called Sanhu 三胡 "the Three Hu peoples". There is therefore no ethnic correlation between these various Hu peoples. The term Hu encompassed peoples speaking Turkic languages, Mongolian languages, Tungusic languages, or, in the Western Territories, even Indo-European idioms like Tokharian.
While the Xiongnu were, at least in the earlier historical phases, pastoral nomads, the Eastern Hu did not only live of hunting but also of agriculture. The Western Hu were settled peoples living in or around citystates with a strong agricultural economy producing cattle as well as grain, vegetables, fruits and silk. Chinese states of the Warring States period located in the north, like Yan 燕, Jin 晉, Zhao 趙 or Qin 秦 did not only have economic and cultural influence on the northern Hu peoples but were themselves influenced by their "barbarian" neighbours. King Wuling of Zhao 趙武靈王 (r. 326-299), for instance, used to wear the costumes of the Hu and waged war in the manner of the Hu tribes, with large contingents of mounted archers instead of the typically Chinese combination of chariots with infantry.
The Han dynasty 漢 (206 BCE-220 CE) founded cavalry units that were staffed with Xiongnu, or Hu (Changshui Hu qi 長水胡騎, Xuanqu Hu qi 宣曲胡騎, Chiyang Hu qi 池陽胡騎). The term Hu was also used for military offices in the protectorate of the Western Territories 西域 in terms like que Hu duwei 卻胡都尉 "commander smashing the Hu", ji Hu duwei 擊胡都尉 "commander striking the Hu", or in honorific titles of nobility for local potentates, like que Hu hou 卻胡侯 "Marquis smashing the Hu", ji Hu hou 擊胡侯 "Marquis striking the Hu" or ji Hu jun 擊胡君 "Lord striking the Hu".
Objects imported from Central Asia were called "barbarian", as can be seen in the designations huqin 胡琴 "Hu zither", hutao 胡桃 "Hu peaches" or hujiao 胡椒 "Hu pepper"; some of these terms are still used today.
During the reign of Emperor Ling 漢靈帝 (r. 167-189 CE) of the Later Han dynasty 後漢 (25-220 CE) "barbarian" clothes, tents, beds, chairs, food, dances and musical instruments were à la mode at the court. After the downfall of the Han dynasty many peoples from the northern zones migrated into China proper and settled down. As long as they were distinct from the Chinese population, they were called "the Hu of Xiutu" 休屠胡, "Hu of Lushui" 盧水胡”, "mountain Hu", "pastoral Hu" 羯胡 or "Hu of Xi" 稽胡. Hu is also a Chinese family name.