What is the different between Meeting Request and Appointment?

I always ask this question when I want to set a personal reminder. So, I decided to figure out what is the different. I open the Microsoft Outlook's help and search for Appointmment. I found there is a help on "About appointments, meetings, and events". This is good enough to tell me how to use these 3 calendar items. Figure 1: Microsoft Outlook's help

In short, the Appointments are meeting schedule that do not involve inviting other people or reserving resources. While a meeting is an appointment that we invite people to or reserve resource for.

The extra thing that I learnt from the help is Events. An event is an activity that lasts 24 hours or longer. Events and annual evetns do not occupy blocks of time in calendar; instead, they appear in banners. An all-day appointment display time as busy when viewed by others, while an event or annual event displays time as free.

The there settings (Appointments, Meetings and Events) are useful when we would like other people who would like to invite us for a meeting request to know whether we are free or busy.