A somewhat old-fashioned or rustic way to address a group of people, often used in period dramas or by older speakers. Can be friendly or slightly formal depending on context.
皆の衆、今日は集まってくれてありがとう。
Thank you all for gathering here today.
Compound of 皆 (みな, 'all') + の (possessive particle) + 衆 (しゅう, 'people'). The exact historical derivation is uncertain, but it has been used as a collective address since at least the Edo period.