Thong underwear or, less commonly, a thong bathingsuit. Synthesis of the English word "fart" (a flatus expelled through the anus) and the German word "halter" (holder). Likely a corruption of the German word "buestenhalter" (brassiere). A synthetic colloquialism visually suggesting that the thong is able to "hold in" the expulsion of a flatus from the user's anus. (Army usage circa 1990)
Check out Specialist Dribble, man. She's wearing the skimpiest färtzenhalter I've ever seen in all my years in Vth Corps!