John,

An event is an item is for an activity that last for 24 hours or longer.
Events do not occupy blocks of time but instead appear as a banner at the
top.  An all day appointment shows busy to others viewing your calendar
whereas while an event or annual event such as a birthday shows time as
free.  Event can be scheduled the same way regular appoint just select the
All Day Event - check box.

Francine Otterson
President, San Diego Outlook User Group