At some point, most stamps are stuck to some paper and mailed off around the world. These stamps are still on their little paper raft!
You will get US and non-US stamps mixed together, and many pieces will have more than one stamp on them.
The neat thing about stamps on paper is that a lot of them have cool cancellations on them.
You will get 40 pieces with at least 40 (but probably more) total stamps.