Q. Define a Formal System?
A Formal System is one which is planned in advance and is used according to schedule. In this system procedures and policies are documented well in advance. A real life instance is to conduct a scheduled meeting at the end of each month in which agenda of the meeting has already been defined well in advance. An Informal System is a system which is not defined by procedures. It isn't used.
According to a schedule. It works on as need basis. For illustration Sales order processing system through telephone calls.