Free-to-play (F2P or FtP) video games are games that give players access to a sizeable portion or to the start of their gaming content without paying. However, players have to make in-game financial transactions to access competitive advantages (like power-ups, money, etc.), cosmetic changes (e.g.: a different type of character/look), or in some cases, to continue playing higher levels.
This is distinct from games which require payment before using the game or service. It is also separate games which are entirely costless. Free-to-play games include, but are not limited to Fortnite, World of Tanks, Valorant, and League of Legends.