Pianterreno means "ground floor".
Primo piano literally means "first floor"
although it corresponds to the "second floor"
it is used to/for ......
it is useful for...
its purpose is to...
it is needed to/for...
The name originated from the first weekly
series of mystery books published by Mondadori Editore.
The cover of these small volumes was yellow and the series itself
was called "I Gialli Mondadori."
The name stuck and now the term "giallo" indicates a
genre of literature and film as well as
real stories reported by the media.
"E' un giallo" is a common expression to indicate
something mysterious, scary and otherwise obscure.