Free-to-Play
Free-to-play (F2P) is a monetization model used by a large number of online games.
F2P virtual economies allow participants to begin playing for free. They may then earn certain types of virtual items or virtual currency. Some items and currency may only be available through a real-money purchase, which is how many games in F2P generate their revenue. Many games also generate revenue from displaying advertising.
Free-to-play is over half the game industry’s revenue as of 2021.
Further Reading
How Virtual Worlds Work, series by Raph Koster, leading innovators of MMOs.