It's the process of changing your mind about something when new evidence on something comes your way.

The different jargon acts as a reminder that the process ought not be an arbitrary one, but (well, in an ideal world anyway) should follow the evidence in a way defined by Bayes theorem.

I don't think there's any particular definition of what constitutes, belief, opinion and cognitive structure. It's all just beliefs, although some of it might then be practised habit.