what are Events in Photos?

If you're going to delete an Album, it is better to remove all the pictures within it before you do so. This will avoid the current bug in Photos where pictures are reported to be in Albums when they are not, because the Album they used to be in has been deleted. See here for more information.

Stephen

Photos 5 on Catalina is automatically splitting the library into Days, Months, Years. The "days" correspond loosely to the old events. But the difference is, that we cannot name them like the events, and we cannot move photos between days. we cannot even pick a key photo for the Days, Months, Years.

It is fully automatic.

They are not duplicates. Photos (like iPhoto before it) runs on a Library principle. Every photo is in the Library. Albums simply contain links back to the library. So yes, you can delete albums and not lose the images.

In Photos, Events are just albums like any other. So, yes you can.

When you migrated from iPhoto your Events were converted into Albums and put in a folder, to ease the transition, that is all.

When you migrate from iPhoto to Photos your Events are automatically converted into Albums. The concept of 'Event' doesn't exist in Photos.