An all day event is an event that lasts most of the day. All day events display at the top of the calendar view. When all day events are created, they are marked as Free. To change the status of an all day event, right-click the appointment, select Show Appointment As, then select how you want the appointment to show.
All Day Events can be used to indicate calendar events that occur on a specific day or days. All day events are useful to indicate annual events such as holidays, anniversaries or birthdays. They can also be used to indicate your vacation schedule or someone else's vacation schedule that might consume more than one day. They may also be used to indicate business events such as conferences, seminars, pay days, or other similar events.