Reading through my recently purchased Sassone Italian specialized catalogue - it certainly is a beautifully done and very informative catalogue, and goes into detail on some of the classic issues.
The meaning of most of the stamp terms is pretty clear without really knowing Italian, but puzzling over the term "decalco". Often used as "decalco della soprastampa" as a variety for overprinted stamps, but also as a variety for non-overprints.
I got a translation of as "decal of the overprint". However, "decal" doesn't make much philatelic sense and web searches haven't helped me much.
I'm thinking it means perhaps over/underinking, or maybe shifted printing? I know it doesn't refer to the position of the overprint. Anyone familiar with the term that can shed light on this?
Although decalco isn't on it, here is a list of some philatelic words translated into several different languages that you may find useful. They are in English, French, German, Italian, Spanish and Portuguese.