A colloquial/slang variant of みなさん (minasan). Used to address or refer to a group of people (everyone), more casual and friendly than the standard form.
みんなさん、今日は来てくれてありがとう。
Thanks everyone for coming today.
みんなさん、次の議題に移りましょう。
Everyone, let's move on to the next item on the agenda.
みんなさんの協力があって助かりました。
I was helped by everyone's cooperation.