Volatility (also known as ‘variance’) refers to how much risk is associated with a game. It describes how often and how much you can expect to win.
High-volatility games reward larger winnings but pay less often. Low-volatility games reward smaller winnings but pay more frequently.
So if you like taking risks and prefer going for big wins then high volatility games are for you. If you prefer being more cautious and playing for a long time, you’ll prefer low volatility games. Medium volatility games offer a compromise between the two.