Japanese, like many other languages, has a large set of terms to refer to different family members (お姉さん, お兄さん, etc.). One special thing about these words is that many of them can even be used to refer to a non family member, including someone you just met on the street and are meeting for the first time.
The term to use depends on the persons sex and age. For example, you would use お姉さん to refer to a young woman. Here are a few of the usages I’ve heard most commonly, with their standard (family) meaning in parenthesis.
- お姉さん – young woman (older sister)
- お兄さん – young man (older brother)
- おじさん – middle aged man (uncle)
- おばさん – middle aged woman (aunt)
- おじいさん – elderly man (grandfather)
- おばあさん – elderly woman (grandmother)
I’d recommend using these when speaking about the person when they are some distance away and not listening to the conversation. For example, if you saw a lady down the street you could say ”そのおばさん、何をしてるのかな？” (I wonder what that lady is doing?)
While you can sometimes use these when talking to the person themselves, I’d be very careful since each of these terms has a connotation about the subject’s age. For example, if you called a young woman (say, 18 years old) a おばさん they would likely get offended. Also, the distinction between the middle aged and elderly women and men is just a lengthening of a sound (i.e. “おじさん” vs “おじいさん”), so even if you aren’t talking to the person make sure you keep your vowels to the right length. (Note: there are some variations of these words which arguably carry negative connotations: “ばばー”, “おばん”, etc.)
While I have seen in some Japanese textbooks that it’s typical to use “あなた” when speaking to a person you don’t know in a foreign setting, I’ve been told by a native Japanese person that あなた has connotations of it’s own so it’s not the best term to use.
So what should you use? Interestingly, I’ve been told that often the safest thing is to just avoid the subject altogether, for example the phrase “お仕事は何をしてるんですか？” (What is your occupation?) as opposed to something that has the subject explicitly stated (i.e. “あなたの仕事は。。。”). Generally when you ask a question in Japanese the listener is the implied subject and adding the subject explicitly could sound awkward.
If you can manage to get their name easily then you can just use that (plus さん) whenever you really need to specify a subject. Of course if they are actually your family member the above terms are safe (and probably best) to use.
One thing that can be confusing is when using the above terms to refer to one’s family member, often the “my” part of “my grandmother” (or “my grandfather”, etc.) is omitted. For example you would say “今日はおばあさんの誕生日だ” (Today is my grandmother’s birthday). However, If you want to prevent confusion you can say “僕のおばあさん” (or use some other first person pronoun like 俺 or あたし), or say “うちのおばあさん”.
Another interesting fact is that お姉さん and お兄さん can be used to refer to a child (in the context of a family) even if they have no brothers and sisters. The connotation here would be that they are a “big girl” or “big boy”. I’ve used this many times with my wife when talking to our son. For example, “もうお兄さんでしょう？” (You’re a big boy now, right?).