So-and-so; used to refer vaguely to certain people without naming them explicitly.
明日の会には田中さんや誰々が来るらしい。
It seems Tanaka and so-and-so will come to tomorrow's meeting.
彼は誰々と親しいらしいが、名前は教えてくれなかった。
He seems to be close with so-and-so, but he didn't tell me the name.
その話は社長や誰々の判断で決まったらしい。
That decision apparently was made by the president and so-and-so.
Used interrogatively to ask 'who?' or 'which people?', a colloquial way to ask about people.
あの二人は誰々なの？
Who are those two?
会場に来ていたのは誰々だと聞いたけど、本当かどうかわからない。
I heard that so-and-so was at the venue, but I don't know if it's true.
昨日話していたのは誰々だったの？名前を忘れた。
Who was the person you were talking about yesterday? I forgot the name.