What are they? Just events from the past...
Some websites use this feature to remind the users what happened on that day years ago.
This is really easy to use and used a block/boxe of the website. You need to activate this feature in the Preferences/settings module.
Select the day, the month, the year and a description of this event. For instance, you can create an event for 10/12/1492. When a user visits your site on 10/12 the left block will display : C. Colombus discovers America.
Select the day and the month, then select the ephemerid you want to edit/delete.
NPDS - Administration manual