iPhotos Album, Smart Album, and Folder differences

Clarkansas wrote: What is the difference between Album, Smart Album & Folder in iPhotos?

I'm guessing you mean Photos-- iPhoto was discontinued 10 years ago.

Albums contain pictures

Folders contain albums or (sub-) folders. Folders do not allow individual pictures that are not in albums.

Smart Albums show pictures that meet your specific conditions. A smart album might have this:

to get pictures of the astronauts taken with a friend's camera.

If you wanted to know which of your pictures were not yet in an album, you could use a smart album, like this:

with Album is not Any

More Info:

When I said "contain," I was being colloquial. In Photos, pictures aren't exactly "in" an album. When you "put a picture into an album," its name is added to a list of pictures from the Library that display together when the album is clicked, kind of like a music playlist, but for pictures. So two albums can both have the same picture name in their lists (like two playlists with the same song,) and that picture will show up when you click either album, but there's only one picture file-- it's just on multiple lists. And when you remove a picture from an album, its name remains in the lists of other albums, and the file still remains in your Library. You don't get fewer pictures in your Library because you remove one from an album; you just get fewer names in the album list.

So albums give a specific view of your pictures. The picture of "Aunt Ethel at the Grand Canyon" can be in the "Aunt Ethel" album with other pictures of Aunt Ethel, and it can also be in the "Grand Canyon"  album with pictures of other people at the Grand Canyon. And it can also be in a the "September 2015" album with other things that happened then. Each album is pointing to a single file stored in the Photos Library, so having pictures in multiple albums takes up no more storage space. As you can imagine, this is very powerful in organizing pictures.

There are special views provided by Apple. The Library View is provided by Apple to give a view of all of the pictures in the entire Library in the order of their "taken" dates or their "added" dates depending on a your menu choice. Removing a picture from the Library View would be deleting it from the Library of Pictures entirely. The Hidden View shows all the pictures from the entire Library that you have marked to be hidden. You can't change how these views work. These albums always provide the same view so that, when something goes wrong or seems off, you (and we) can depend on them always showing the same thing, and there's no chance that someone snuck in and changed the order or removed pictures. 

By the way, Recently Deleted is also just a special view of all the pictures in your Library that you’ve marked to be erased. The names of those pictures are still on the album lists; they’re just not shown. If you “restore” a picture from Recently Deleted, then they are shown again in the albums that had listed them. Hidden is similar— the names are still in the album lists, so when you un-hide a picture it shows up again in all the albums it had been in previously.

Too much information?

You are certainly welcome!