Traditionally, pay to win refered to a situation in a videogame where paying real life money gave the player any sort of advantageous or otherwise gameplay-altering (non-cosmetic) effect or object. These could range from acquiring regular in game items that can be obtained easily through regular gameplay to powerful items and
advantages via the use of real money, whether exclusively or not.
Nowadays, the meaning of the expression varies slightly. It is mostly used to describe games which either have significantly powerful
perks or items exclusively obtained with real money or excessively
grindy games where the advantage obtained by using real money can be accomplished through gameplay, albeit taking very long to obtain.
Some players argue that pay to win only applies to online games, in which paying real money can give players an edge over players who simply play the game in order to unlock more weapons, characters,
progression, etc. while others consider it can apply to any kind of game (including
single player titles) where paying real money gives an advantage to the player.
Games which merely offer some minor advantages (in game objects, currency, experience boosts...) via
microtransactions,
DLCs or other bonuses are regarded by most as not pay to win, even though they technically fit that description in the traditional sense, since they are still considered advantages tied to real world money.