noun
so-and-so; a certain person
Used as a placeholder for an unspecified or intentionally concealed person's name, similar to 'Mr. X' or 'so-and-so'. Often appears in formal or written contexts.
契約書には某々と記載されていた。
The contract listed the name as 'so-and-so'.
某々氏がその役職に就任した。
A certain person (Mr. So-and-so) assumed the post.
某 is a prefix or standalone noun meaning 'a certain...' and is more common in modern usage, while 某々 is a reduplicated form used specifically as a placeholder for a person's name.
Reduplication of 某 (ぼう, 'a certain person'), used as a placeholder name. The exact historical derivation is uncertain, but the form is conventionally associated with concealing or generalizing a person's identity.