1. μΈλ/λλ π―ββοΈ
So this is probably one of the common ones that you've all already heard before! μΈλ (eonni) and λλ (noona) both mean older sister! BUT are actually very commonly used for non-family members! β€οΈ
The difference between the two terms is that μΈλ is what you would call a female who is older than you -- if you are also a female! λλ is used when you are a boy referring to a girl who is older than you. These terms are very commonly used BUT make sure you are using them correctly. You would RARELY call someone this right off the bat, and it would usually come naturally if you guys are super close friends! There is also a possibility that someone you meet, when you say their name -μ¨ will just be like "call me μΈλ, or call me λλ" as in "you can drop the formalities!" π
You'll often hear the phrase "μλμΈλ" which is technically like "an eonni I know!" How do you differenciate? When you're talking about your real family you would add "-μΉ" in front of it. If I was introducing my older sister I would say she is my μΉμΈλ!
This would only be used if you're close and it is a mutual understaning but the only case that μΈλ is used otherwise is by shopkeepers! Weird, I know! BUT if you visit a store or even nail shop, the shop-keepers will sometimes call you μΈλ regardless of your age! No need to get offended, it is very friendly π
The term λλ is used in this clip below~ see if you can find it :) | 
