Junk is classified as anything that isn't armor, weapons, ammo, plans, notes, bobbleheads, magazines, and other classifications; the main difference is that they are primarily salvageable for more empirical junk. Wonderglue, duct tape, Giddyup Buttercup pieces, hot plates, wrenches, screwdrivers, and other such junk-like items count as part of this, and you'll want to scrap all of this later on anyway.