Casual male greeting between close friends, similar to 'hey' or 'yo'. Not used in formal settings.
Yo, how's it going?
yes sir; understood
Used in martial arts or similar hierarchical settings as an energetic affirmative response, like 'yes sir!' or 'understood!'.
"100 push-ups!" "Yes sir!"
Ateji spelling; the standard written form for this greeting.
The exact origin is uncertain. It is often said to be a contraction of おはようございます, but this is not confirmed. The kanji 押忍 are ateji.