Collecting

One major collectable category is Souvenir Sheets. they've been around for quite a while, but in recent years there have been more and more of them. as with many things in the world of stamp collecting, they're less about postage and more about the collection.

Here is souvenir sheet from the US in 1947, commemorating the first US postage stamps.



Note that the stamps embedded in the sheet are valid for postage, you can cut them out and use them, or put the entire sheet on a package. But they're imperforate, you have to cut them out to use the individually. Early stamps were commonly imperforate.