According to a blog posting at AbeBooks (and widely copied around
the Internet, including here):

  "The term leporello refers to printed material folded into an
accordion-pleat style.  Also sometimes known as a concertina fold,
it is a method of parallel folding with the folds alternating between
front and back.

  "The name likely comes from the manservant, Leporello, in Mozart's
opera Don Giovanni.  Famed rogue and lover Don Giovanni (in Italian --
also known as Don Juan in Spanish) has seduced so many women that when
Leporello displays a tally of his conquests, it unfolds, accordion-
style, into a shockingly long list.  Many leporellos are used as a way
of telling a story, while others are purely visual."

Source:
https://www.abebooks.com/blog/2013/05/16/leporello-and-concertina-books 

Elsewhere on the 'Net I read that the folded leporello book appeared
shortly after the introduction of inexpensive chromolithography in the
late 1800s.  Also known as concertina book or (nowadays) Z-fold book.

Robbie Rhodes
Etiwanda, California