The full form of pms is Piedmontese. It’s used on Regional ,Language Codes in Italy

Piedmontese (ISO 639-3 language code: pms) is a Romance language spoken by people in Piedmont, northwest Italy.

Piedmontese (autonym: piemontèis [pjemʊŋˈtɛjz] or lenga piemontèisa, in Italian: piemontese) is a language spoken by some 700,000 people mostly in Piedmont, northwestern region of Italy. Although considered by many linguists a separate language, in Italy it is often regarded as an Italian dialect. It is linguistically included in the Gallo-Italic languages group of Northern Italy (with Lombard, Emilian, Ligurian and Romagnolo), which would make it part of the wider western group of Romance languages, which also includes French, Occitan, and Catalan. It is spoken in the core of Piedmont, in northwestern Liguria, near Savona and in Lombardy (some municipalities in the westernmost part of Lomellina near Pavia).