In simple terms, "pure junk" means something that is completely worthless or of extremely poor quality.
Sentences with «pure junk»
If you're after pure junk food, vegan style, this is the place to go and I'd recommend the barbecue burger with hot - scharlotte sauce and nothing else, tasted like the real deal to me (minus the blood). (goodeatings.com)
While these leftovers don't pose a threat, they are pure junk data, and an ideal antivirus or malware - removal program should get rid of everything installed during a malware infection, not just the active components. (tomsguide.com)