"Free-to-Play" (F2P) is the phrase used for both single and multiplayer games. The idea is, you get to download a game and play it for free, but you have to kick in cash in order to unlock "special" items such as weapons, abilities, clothing and items that change the appearance of your in-game character, and others.
In nearly all cases, you use real money to buy virtual money, coins, tokens, or whatever the in-game currency is called. They're all the same. Real money essentially gets translated into game money.
The following is just an example. It's not based on any actual game available at the time of this writing:
You'll see "great deals" like "$10 (USD) for 2,500 coins!" You think to yourself, "That sounds like a great deal! I get 2,500 'somethings' for 10 bucks! That's only $1 for 250. Great deal - if I buy 4, I'll have 10,000 coins!" That's where the disconnect begins. What is the true value of a "coin?"
Once you go to the game's store where you "buy" your in-game items with the virtual currency, you won't see items using real-world currency values. Nope - you're in the virtual currency world where that "kill em all with fire" ability costs a mere 7,500 coins. You buy it without even thinking that you just spent $30 on one thing. That is how the publisher of the games make their money. In some cases, you could spend hundreds of dollars on a single game in the form of these "micro-transactions" of virtual currency.
What's worse, some of the F2P games fall into another category - "Pay to Win." With this model, the game is designed to be difficult, or in some cases impossible, without "buying" an in-game item to pass a certain level or beat a particular boss. You won't find this advertised anywhere, of course. I find these types of games predatory and frankly, ridiculous. There's a well-known electronic publisher of games with a two-letter name that falls into this artful model for most of their newer F2P games, and shame on them for it.
I'm not saying I recommend completely avoiding F2P games. There are a lot of great ones out there well worth a few bucks here and there. If you visit the in-game store of a F2P game and buy items, do the math. What is that coin really worth? Also, watch your budget. Don't spend $200.00 on a game that could have easily retailed for $50.00 as a non-F2P title. In summary: Developers deserve to be paid for their creations. Just don't break your own bank in the process.
To see a F2P game done correctly, check out today's YouTube Video (MG's Let's Play Loadout - Ep 1: Welcome to the Machine) where I play a relatively new F2P game on Steam called Loadout. The game is a ton of fun, well-balanced, and not in the "pay to win" category. If you haven't checked it out yet, go fire up Steam and download it. We'll be here waiting. Go ahead. It's worth it.