Ad Hoc meetings - a once off meeting help discuss and solve immediate problems that have arisen
AGM - a meeting held once a year involving directors, shareholders of a firm discussing events of the previous 12 months and future plans
EGM - a meeting of shareholders to discuss important matters that cannot wait until the next AGM
Board of Directors meeting - the purpose of the board meeting is to get a pulse on the entity and to do a check-in on the health and profitability of the company or non-profit
formal meeting - such as a staff meeting - pre-planned
informal meetings - takes place regularly as staff members bounce off each other and listen to each other's views