Question: What does “PIE” mean?

Answer: “PIE” is a table rule that restricts the maximum amount a player can lose during the game, usually $5. Once a player’s coins are depleted, they can continue playing without incurring further losses. They only need to contribute to payouts once they start winning again.

Some players say that “PIE stands for “purse is empty”. The league calls it a “PY” but, no one knows why. This ruling is not found in Mah Jongg Made Easy.

(See also https://mahjcon.com/mahjpedia/id53)

Source:  National Mah Jongg League Bulletin (1967)