This is the 82nd most frequent Korean word.
씨는
"씨는" is a combination of "씨" (a polite suffix for names, like Mr./Ms.) and the topic marker "는" in Korean.
Here, '씨는' is used to address an individual respectfully as 'Mr.' or 'Ms.' followed by the surname.
김 씨는 한국에서 태어났습니다.
Mr. Kim was born in Korea.
In this context, '씨는' introduces the topic, using '씨' after the name for politeness.
철수 씨는 내일 약속이 있습니다.
Cheolsu has an appointment tomorrow.
This shows '씨는' stating a fact about a person, with '씨' adding honorific respect before describing the characteristic.