1. What does it mean?
알바 is the everyday shortened form of 아르바이트. It can refer to the work, a shift, or a part-time worker, with the intended sense usually clear from the sentence.
Also written or said as 아르바이트, alba
2. The nuance
It is distinct from 알 바, 'something to know or care about,' despite the similar sound. In an online argument, calling someone an 알바 can also insinuate paid advocacy without proof.
3. Examples
“주말에는 서점에서 알바해.”
I work part-time at a bookstore on weekends.
“오늘 알바가 늦게 끝나서 약속에 조금 늦을 거야.”
My shift ends late today, so I'll be a little late to our plans.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.