Breakdown of Hallo, wo bist du?
sein
to be
du
you (informal singular)
wo
where
Hallo
hello (informal, any time of day)
Questions & Answers about Hallo, wo bist du?
Why does wo mean "where"? Doesn't it sound like "who"?
This is a very common mix-up for beginners! In German, wo means "where", and wer means "who". They are false friends because they look and sound a bit like their English opposites. Just remember that wo asks about a location.
Is bist a regular verb?
No, bist comes from the verb sein (to be). Just like in English (I am, you are), it is highly irregular. bist is the specific form you always use with the informal "you", which is du.
Could I use this exact sentence to ask a stranger where they are?
You probably shouldn't! This sentence uses du, which is the informal "you" meant for friends, family, and children. If you are speaking to a business partner or a stranger, you would use the formal "you" (Sie) and ask: Wo sind Sie?
Is the word order here the same as in English?
Yes, in this case it matches perfectly! In German questions that start with a question word like wo (where), the verb must come second. So we have our question word (wo), followed by the verb (bist), and then the subject (du).