This is the 14463rd most frequent Korean word.
문승원이
"문승원이" is not a standard Korean word; it appears to be a proper noun, likely a person's name.
The word "문승원이" is used as a proper noun here, identifying a person by their name followed by a subject particle to indicate that they are the topic of the sentence.
문승원이는 오늘 학교에서 발표를 했어요.
Moonsungwon gave a presentation at school today.
The word "문승원이" functions as a possessive form (with the additional marker "의"), indicating ownership and describing the study methods as belonging to Moonsungwon.
문승원이의 공부 방법은 정말 효율적이에요.
Moonsungwon's study methods are very effective.
Here, the word "문승원이" is used with the directional marker "에게," indicating that the action of writing a letter is directed toward Moonsungwon.