Why do pilots say papa?

Excuse me, could you please elaborate on the reasoning behind pilots using the term "papa" in their communications? Is it a historical convention, or does it serve a specific purpose in aviation terminology? I'm curious to know if there's a standardized reason why they choose this particular word, and if it has any significance beyond simply being a code word. Could you provide some insight into the origins and usage of "papa" in the world of aviation?