Pay what you want, or PWYW, is a pricing option and publishing model in which consumers of a good, most commonly a digital publication, can choose how much they want to pay to the author or publisher, including nothing.
Offering an RPG product as pay what you want may mean that more people "buy" or download it, but it also risks devaluing the work involved and has no guarantee that everyone who downloads it will use it in a game. A small number of publishers use PWYW goods as part of their business model, e.g. Evil Hat Productions' Fate Core.