In that case, the original meaning of '백수' is a bare hand, which implies s/he has nothing. So. we use this word when we call a person who is penniless but doing nothing and idling.

https://ko.dict.naver.com/#/entry/koko/1155f703703742a1a10e3d294eb3bc15 Here's the link for you. You could find it at the entry #2. Like the link says, 백수 came from 백수건달(돈 한 푼 없이 빈둥거리며 놀고먹는 건달). But actually I heard they don't have any concrete consensus about from what word the 백수 really originate. The literal meaning of chinese character for the 백수 is just "white hands", and I think it's because if they don't have anything to do, their hands wouldn't get dirty or what not. In fact, they've long since been using some words that mean colors of hands to refer a person's financial(?) state. Such as, 적수공권(Red hands empty fists), which means having nothing in their hands literally, is another case. As for the alternatives... You would say... 무직자: When you deal with some kind of formal documents you use this word. 취준생(취업준비생): When someone is looking for a job, especially that person just took a first step to the real world. 구직자: More formal version of 취준생, and not just a young people. 고시생: when you are preparing a national exam 실업자: recently got fired. 한량: jobless but live it up cos they have a lot of money But I suppose 백수 is quite enough to use all the time unless you use it to other people sarcastically. The safe way to choose is just saying it without exact words. Such as... "저 사람 일 쉬고 있대" "나 지금 그냥 좀 쉬고있어" "직장 안다녀요"