* It's a misspelling: Could you be thinking of a similar-sounding word? Perhaps provide more context (where you encountered this word, what it refers to).
* It's a dialectal word: Greek has many dialects, and a word might exist in one that isn't widely known.
* It's a loanword: It could be a word borrowed from another language and used informally in a specific context within a Greek-speaking community.
Without more information, it's impossible to say what "papia" might mean in Greek.