Cheating on your wife or girlfriend, especially if in the process of cheating, you disappear for a few days and say you are going someplace where it is impossible to be reached. Can also be used on a woman to say that she's cheating.

Same meaning as the other two entries here at UrbanDictionary.com: "Hiking in Appalachia" and "Hiking in the Appalachian Mountains", except that that "hikin' the Appalachian Trial" sounds better.
guy 1: "Where's Dave? I thought he he was going to play golf with us today."

guy 2: "He told his wife he had to work the weekend, but I think he's hikin' the appalachian trail. He was flirting all week with that new chick in accounting"

-or-

guy 1: "Where has your girlfriend been lately?"
guy 2: "I dumped her ass! Caught her hikin' the appalachian trail, and that was it for that slut!"
by rpompeii June 29, 2009
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