mǒu​mǒu

so-and-so

某某 mǒu​mǒu
so-and-so pronoun
a placeholder used to refer to a person whose name is unknown or intentionally withheld

A Mr. So-and-so just called for you.

such-and-such pronoun
a placeholder used to refer to a thing, place, or situation that is not specifically named

He worked at a certain company for ten years.

Frequency

Movie subtitles
1.10 per million appears in 0% of films
Written text
6.47 per million

Sources

Definitions
CC-CEDICT