What is Ephemera?

The Ephemera Society defines it as such:
advertisements air transport labels bank checks baseball cards billheads bonds bookmarks bookplates broadsides brochures business cards calendars cameo stamps
chromos cigar box labels bands clipper ship cards die-cuts greeting cards
indentures invitations labels letters magazines maps newspapers packaging pamphlets paper dolls passes photographs postcards postage stamps posters programs rewards of merit seed company ads Shakers sheet music songsters stocks tickets timetables trade cards trade catalogs valentines watch papers

Now, that isn't a definition as much as a list to help you define it for yourself. 
I argue that anything that is temporary or of a very short life span can be considered ephemera.  When we first started using the Evergreen open source software for our library's circulation system, the icon for uncataloged magazine and paperbacks was a ghost.  I think that has unwittingly influenced me.
I italicized the things I like. Maybe I'll link them to actual examples of items I've cataloged. later. I bolded the things that mystify me. I'd also like to know if the Shakers they refer to, being the only proper-noun-looking-because-it's-capitalized-word, are the religious sect, the celibate ones, that don't actually exist anymore. WOW. Collecting souls. Had no idea. Creepy.

If they meant SALT and PEPPER shakers, why did they pronoun-icize it?
If you click on the photo it will take you to the Ephemera Societies website where you can then explore their links to specific collections/collectors.

Note 09/18/09: I found definitions and examples of the bolded items that aroused my curiosity.  The watch papers is, to me, a perfect example of a collectible, catalogeable piece of ephemera.  Rare, strange and small.  Like me.