Romanized Popular Alphabet
The Romanized Popular Alphabet (RPA) or Hmong RPA (also Roman Popular Alphabet), is a system of romanization for the various dialects of the Hmong language. Created in Laos between 1951 and 1953 by a group of missionaries and Hmong advisers, it has gone on to become the most widespread system for writing the Hmong language in the West.
Source: Wikipedia — Romanized Popular Alphabet (CC BY-SA 4.0)