A semi-formal meeting the public is typically invited to attend and listen to the speakers. Semi-formal meetings use some of the procedures of a formal meeting.
Formal meetings are preplanned with a specific set of topics to be discussed and certain objectives as well as a specific agenda. Informal meetings are not as planned out as formal meetings and are often last minute meetings.
In a formal meeting, you say, "The meeting is adjourned."
In the context of a formal meeting, an 'apology' refers to prior request to be absent from a meeting. It simply means, that the members are aware of your absence.
Formal and Informal.
It depends on what you mean when you are referring to as a formal meeting.
A formal meeting is a preplanned meeting. It has a predetermined set of topics that one wishes to discuss along with a set of objectives that one wishes to achieve at the end of the meeting. At a formal meeting, generally it is a senior executive who presides over the affair. The members of the meeting are often given a considerable period of notice before the meeting, preferably through formal means such as memos. As the title suggest, the atmosphere in such meetings is generally somber, formal. Informal meetings are generally not planned well in advance. The members are not notified through formal means. They generally take place in neutral surroundings, for example in a restaurant rather than a boardroom.
convene
lobsters backs
so they can get busy
for example curry is a fomal activity office meeting
By following the formal meeting procedures established by the project or company having the meeting. Been to thousands of them over my 30 year career.