This is the 274th most frequent Polish word.
oni
"They" (masculine or mixed-gender plural pronoun).
refers to a group of men or a mixed-gender group.
Oni zawsze idą do parku.
They always go to the park.
indicates a polite or respectful way of referring to a group one is discussing or querying about.
Czy oni wiedzą, gdzie jesteśmy?
Do they know where we are?
emphasizing the subject 'they' in the context of the narrative.