TOPIC: Are meetings considered Informal or formal?

I've seen explanations to sample questions in other commercially available resources that indicate "meetings are classified as informal verbal", but the PMBOK guide (p. 92) reads "Meetings may be face-to-face, virtual, formal, or informal."

Are meetings always considered informal verbal? If a PM is holding a status meeting with stakeholders of a large project, is this considered formal verbal or informal verbal communication?

The two types of meeting mentioned in PMBOK are user groups and review meetings. I think that USER groups is informal and Review meetings would be formal. The PMBOK guide itself is vague or generic in their references but it is possible that more examples are needed to determine what is formal and informal.

I would imagine the primary difference between formal and informal meetings would be how structured they are. For example, a weekly team meeting with a pre-determined agenda, set time and location, and meeting minutes recorded would be a formal meeting, whereas a quick ad hoc conference call between project members to clarify something that was previously discussed might be considered informal. I don't know that there is any hard and fast definition, though, nor do I recall any focus on this distinction on the exam or any prep materials I encountered.

From page 295 of the PMBOK Guide (5th Ed): "Although causal discussions may be construed as a meeting, most projectmeetings are more formal with a prearranged time, place, and agenda." This seems to suggest that both types are possible (though formal is more common).