"Pay-to-win" or "P2W", is a pejorative term for a game that offers any advantage that can be obtained faster or exclusively via commercial transactions over gameplay rewards or the impact of the player's own performance.
This market practice is seen negative because it destroys the sportiveness of games, rewarding mediocre players who look for an easy way to beat the competition or the challenge, instead of promoting fair play.
Imagine, for example, an Archery competition where the archers could optionally buy the right to use laser-dot scope aims in their bows Every archer would look to exploit that artificial advantage, instead of actually improving themselves at the sport.
"I dont play pay-to-win games. It's a waste of effort and I rather use the money to buy real games".