‘In’ a meeting or ‘at’ a meeting? Which one is correct? [duplicate]

I would like to know what preposition ‘meeting’ should take. Should I say I’m at a meeting or I’m in a meeting?


In my opinion the difference lies in actively and passively participating.

In a meeting means you are actively participating in the meeting.

"I'm busy right now. I'm in a meeting."

At a meeting means you are present at a meeting but not necessarily participating.

"When you are at a meeting you have to talk quietly when taking a phone call."