Polite term for one's own older sister or someone else's older sister. Honorific (sonkeigo).
See also: 姉さん
お姉さんは大学生ですか。
Is your older sister a university student?
My older sister is good at cooking.
Vocative use to address or refer to a young woman politely, similar to 'miss' or 'young lady'.
See also: 姉さん
Excuse me, miss, is this seat taken?
Only when written お姐さん
Used to address or refer to a waitress or female service staff. Often written お姐さん.
See also: 姉さん
Miss, could I have some water, please?
older girl
Refers to a girl older than the speaker, often in a school or neighborhood context. Less common than the 'older sister' sense.
An older girl in the neighborhood helped me with my homework.
Excuse me, miss, could you tell me the way?
Miss, could I get some water, please?
お姉さん is the polite, everyday term used to address an older sister or an unfamiliar young woman, whereas 姉ちゃん sounds more familiar or rough.