An unofficial US Navy term. An area in a continental European city where the trashy bars and prostitutes usually are. This area is typically listed as "off limits" to all Department of Defense personnel, but is usually where you run into the Command Master Chief, or the CO.
"Hey Sailor, where are you going today?"
"I'm headin' to Four Floors o' Whores, Master Chief"
"Sailor, that is in The Gut and off limits!"
"I'm payin' for the rounds o' drinks, Master Chief"
"Wait right there Sailor. Let me get my civvies on"