What is a “sandwich thesis”? On the Internet, I have found that some people have graduated with a PhD by means of a “sandwich thesis”. Could anyone explain what it is?
I believe that a sandwich thesis (sometimes called an integrated thesis / stapler thesis) consists of a collection of published or in-press articles (some schools also allow submitted articles). These articles are included in the thesis verbatim.  The publications are usually preceded by an elaborate introduction that sets the context for the thesis.

EDIT:

As Willie Wong pointed out,  there is also usually a final discussion / conclusion after the integrated papers.