1. What does it mean?
ㅈㅂ uses the initials of 제발. It can beg for a result, ask someone to stop an annoying habit, or add urgency to a request in a casual message.
Also written or said as je-bal
2. The nuance
It is not automatically polite just because English translates it as 'please.' 제발 itself can sound desperate or irritated, and abbreviated wording is unsuitable for a formal request.
3. Examples
“ㅈㅂ 이번에는 저장한 파일이 제대로 열려라.”
Please let the saved file open properly this time.
“방 안에서는 ㅈㅂ 스피커 말고 이어폰 써 줘.”
Please use headphones instead of the speaker in the room.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.