This is the 3924th most frequent Korean word.
오래된
"오래된" means "old" or "aged."
Here, '오래된' is used as an adjective to modify the noun 'book' (책), meaning that the book has existed for a long time.
이건 오래된 책이에요.
This is an old book.
In this sentence, '오래된' describes the friendship's duration, indicating that the friendship has been long-standing.
저는 오래된 친구를 만났어요.
I met an old friend.
The phrase '아주 오래된' is used here to emphasize the antiquity of the building, adding an adverb ('아주') for intensity.