P2P, Pay to Play: Buy the game and spend money (usually monthly) to keep your account active. Ex: Aion, WoW, Rift, SWToR
- Usually has a online service shop to buy things online for extra money, like server change.
- Don't usually charge for extra content (not counting expansions)
F2P, Free to Play: Download game and log in to play with a free account. Ex: Runescape, League of Legends, Vindictus
- Usually has a 'members' account type system to unlock many extra features in game
B2P, Buy to Play: Buy the game and from then on the game is free. Ex: Guild Wars (not sure who else has this)
- Usually has a online shop for cosmetic items, or extra things in game (extra character slots, extra hair styles or other character customization)
- Comes out with expansions regularly
Hope this helps people realize why saying it's F2P is wrong, or saying that it is P2P because you buy the game~