Noun: A young, inexperienced, fresh-to-the-fleet Marine, who's still crapping out MCRD chow, still thinks High-and-Tights are cool, wears a stupid digi-backpack, and has not yet paid off their G.I. Bill.
From the combination of 'Teufel Hunden' (German for Devil Dog, and a common nickname for Marines) and 'boot', which denotes a young, inexperienced Marine.
Senior Lcpl: "Hey, who's that with the USMC shirt and the cammie pack out in the quad doing PT on a Saturday?"
Other Senior Lance: "Oh, that's some stupid-ass Teufel Booten...want another beer?"