a formal one is "Ni Hao". “美眉" or "MM" means beautiful girl(s) ”恐龙“ or "猪扒" means ugly girl(s) They are kind of new words from Internet or other Medium. and depends on different situations. There can be a number of ways of expressing a greeting in Mandarin: "ni hao ma?", - How are you? "zenme yang?", - How is it going? "zuijin hao ma?", - How have you been recently? "jinlai hao ma?", - How have you been? "chi fan le ma?", - Have you had your meal? "hao jiu mei jian le!", - Long time no see ! "ni qu nar le?", - Where have you been? "zao wa!", - Good morning ! "zao an!", - Good morning . "wan an!", - Good night.

ni hao = hello or nin hao

ni(2) hao(3) - "hello" if you greet someone older than you, you would basically say: nin(2) hao(3). :)

美眉(mei3 mei2) is a SLANG word only used by SOME young people. usually used by young men greeting girls. it's VERY informal.

美眉 originally is used over the internet by Chinese people..Gradually became popular in everyday life as well. If we greet some girl or young lady for the first time on an informal occasion, we would rather call her 美眉 which means "beauty" ,even though she is not beautiful. But mostly every lady would be glad to hear herself being called beauty.....That's a woman!