Short for free-to-play, F2P is a type of game that doesn't require any monetary contribution from players for them to participate. However, to support the game's continued development, it may have advertisements or require payment or a subscription for higher levels, items, or other game features.
Although some may use "FTP" as an acronym for "free to play," it should be avoided to prevent confusion with FTP (File Transfer Protocol).
What is free-to-start?
A free-to-start game allows a player to participate up to a certain point before requiring payment or a subscription. You think of this as a "free sample" of the game. A good example of a free-to-start game is WOW (World of Warcraft), where users can play up to level 20 before needing a subscription.