This is the 4749th most frequent Japanese word.
某
"某" means "a certain" or "someone unspecified."
某 is used to indicate a certain unnamed or unspecified person, in this case, a teacher.
某先生が新しい本を出版したそうです。
A certain teacher published a new book, it seems.
某 is utilized to refer to an unnamed location or place.
昨日、某場所で不思議な出来事があった。
Yesterday, at a certain place, a mysterious event happened.
某 here signifies an unspecified organization, keeping its identity anonymous.