interjection
yes sir; understood
Used in martial arts or similar hierarchical settings as an energetic affirmative response, like 'yes sir!' or 'understood!'.
「腕立て伏せ100回！」「押忍！」
"100 push-ups!" "Yes sir!"
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.