* बहिनी (bahini): This is the most common and general term for "sister". It can be used for any sister, regardless of age.
* दिदी (didi): This term is used for an older sister. It's similar to "sis" or "big sis" in English.
So, if you are talking about your younger sister, you would use "बहिनी". If you are talking about your older sister, you would use "दिदी".