A somewhat formal or old-fashioned way to address a group, often used in speeches, announcements, or historical contexts. Can sound dramatic or ceremonial in modern conversation.
Everybody, listen carefully.
The lord said, 'Gather round, everyone.'
Compound of 皆 (みな, 'everyone') + の (possessive particle) + 者 (もの, 'person'). Literally 'people of everyone', used as a collective address.