This is the 17170th most frequent Korean word.
서른
Thirty.
In this sentence, '서른' is used to denote the age of 30, showcasing its use as a cardinal number representing an age.
저는 서른 살입니다.
I am thirty years old.
Here, '서른' quantifies the number of apples, meaning 30, emphasizing its function as a numeral for counting objects.
서른 개의 사과를 샀어요.
I bought thirty apples.
In this sentence, '서른' is combined with '번째' to form an ordinal number, indicating the thirtieth iteration of an event, a birthday in this case.