A rural area far from large towns, and somewhat behind in development. Sometimes used to describe somewhere very conservative people and/or small minded people live, or a place in the countryside with little modern comforts.
You don’t want to drive all of the way there to visit Billy, he lives out in the boonhickey!
That is Soo Boondockey! (A guy just Drank Human and Rat Urine at the same time. He then Threw Up saying " That is the most boondockeyest thing I ever done!!"