오래된

In a sentence

• 이건 오래된 책이에요.

  This is an old book.

  Here, '오래된' is used as an adjective to modify the noun 'book' (책), meaning that the book has existed for a long time.

• 저는 오래된 친구를 만났어요.

  I met an old friend.

  In this sentence, '오래된' describes the friendship's duration, indicating that the friendship has been long-standing.

• 그 건물은 아주 오래된 것처럼 보여요.

  That building looks very old.

  The phrase '아주 오래된' is used here to emphasize the antiquity of the building, adding an adverb ('아주') for intensity.