(1) So "Yo" is a greeting, as when two hikers meet. "Yo-yo" is a double greeting, one that you can give to yourself by first reaching the end of the trail, and then really quickly turning around and starting back the way you came so fast that you bump into yourself. Swearing works too.
(2) Even if you're not fast enough to execute a one-person collision, you can still use "yo-yo" to mean hiking from one end of a trail to the other, and then hiking back to where you started. Some people do this over really long trails, if they have a whole lot of time to kill and no imagination.
(3) A stupid person. (What was your first guess? See previous definition.)
(4) Someone with nothing better to do than to hike a trail, and then turn around and do it again in reverse. This person may be a yokel (a yo-yo mechanic) on vacation. Or may have left his wallet back there. That happens too. But there are lots of reasons why this can happen, all of them uninteresting.
(5) Walking from one end of the trail to the other, then turning around and walking back. May become part of a hikers name, as in "Yo-yo Dumbnuts." Also used as greeting by those who think they are cool. Meh. No.
(6) Etc.: "Yo-Yo Hike", "yo-yoing", "yo-yoer". Yawn. Enough already. Let's get out of here.
Have anything worth adding? Then try sosayseff+eff@gmail.com
Me? Tried yodeling but got all tangled up in the string.
Etc...
so says eff: sporadic spurts of grade eff distraction
definitions: outdoor terms
fiyh: dave's little guide to ultralight backpacking stoves
boyb: dave's little guide to backpacks
snorpy bits: nibbling away at your sanity
last seen receding: missives from a certain mobile homer
noseyjoe: purposefully poking my proboscis into technicals