Some free-to-play games are actually freemiums or pay-to-win in disguise. One short definition for freemiums is:

https://en.wikipedia.org/wiki/Freemium
All or most features are available for free, but require extended unlocking or slowly obtained in-game currency which can be accelerated or purchased for a fee.

If the game has Player vs. Player combats, then it can easily turn into pay-to-win game if it's not properly
designed. Those who spend more money will get better armor, weapons, abilities, ...

https://en.wikipedia.org/wiki/Freemium_Isn%27t_Free
"Freemium Isn't Free", the sixth episode in the eighteenth season of the American animated television series South Park satirized this business model.