Going hiking here in Japan, you can hardly pass anyone without either saying
お疲れさまです, おはようございます (I go hiking in the morning) or こんにちは.

Some people (young males in particular) greet you with either チュワッ or オッス. A
great idea, since everybody's out of breath. I gather that チュワッ is a
contraction of こんにちは, but オッス could be either お疲れさまです or おはようございます. Does the
person greeting you with オッス actually have one of the two possible greetings
in mind, or is it just used more like a universal sound, which can be used in
any situation?
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spoken-language
おっす！ An abbreviation for ... what exactly?
It might have been おっす instead. According to [gogen](http://gogen-
allguide.com/o/ossu.html), it's おはようございます that has undergone shortening to
form おっす.
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I've often heard "おっす" as a shorter version of "おつかれさまです". That'd be a
greeting you'd say after someone had a tough day, a long ride, or almost
anything.

It can also be used is a very derogative sentence "人生おっす!" (jinsei, oss(u)!"
which I reckon is something like "thank you for living until today, you now
useless piece of (…)"

Notice that in both cases, I think that it is _extremely_ informal, if not
vulgar.
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It is おはようございます. When I was in university, students would often say it to me
and I had to ask what it meant.

They would also say ちっす for こんにちは and わっす for こんばんは, but I think those are
more slangy.

A similar one I often heard was あざっす for ありがとうございます.
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2012-09-14T02:24:00.940
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There are a number of ideas for the origin of おっす. I first learned this term
as rough greeting used by men to each other in Karate school, and had thought
it quite manly till I heard a cute girl say おいっす in a joking fashion. Besides
the contraction of おはようございます as stated in the other answers, there is a more
martial origin listed as well:

> Osu is a contraction of the words:
>
> 押し Oshi meaning "Push"
>
> 忍ぶ Shinobu meaning "to Endure"
>
> It means patience, determination and perseverance. Every time we say "Osu",
> we remind ourselves of this.

My own two cents: I have seen guys say this to each other as a greeting in
bars at night, where I would not hear おはようございます.

Here is a link to two in-depth discussions:
<http://tkdtutor.com/TOPICS/Concepts/Concepts/Osu/Osu-01.htm>

<http://uskyokushin.com/osu.htm>
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My personal opinion on this (not backed up by any evidence) is that many of
the greetings end in す and I find that even when most people tend to say the
whole greeting you only tend to hear the last す syllable as people tend to
start quiet and get louder. My guess was that this written approximation, おっす,
came from there.
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2012-10-25T09:44:04.010
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According to my dictionary (ウィズダム英和・和英辞典) 「おっす」 means

> Howdy!; Hey (there)!; Hi!; ↗Morning! (!いずれも通例, 後に相手の名前をつける.
> 後になるほど「おっす」から「やあ」「おはよ」ぐらいの意になる)

Unfortunately, it does not give any etymological explanation, though.
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2013-03-13T00:49:31.657
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From what I've learned, it comes from Judo. From experience, it is an
extremely informal greeting used ONLY by males that is more of a joke than
anything else. Similar to "Yo!" or "Yo, man!"

Oh!sssss.... oo!sssss.....
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