Confusion about Huns, Northern Nomads, or Mongolian Nomads.

This source describes the Huns as the major enemy of the Ancient Chinese empires. Other sources say "Mongolian Nomads" or "Northern Nomads". Are these the same thing? Is one more correct than the other? I'm confused a great deal about this and I am doing a paper of the development of the Great Wall, so I want my information to be accurate. Any feedback would be much appreciated. Thanks!