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 receive in rewards.
High-volatility games provide larger payout sizes but deliver them less often. Low-volatility games provide smaller payout sizes but deliver them more frequently.
So if you like taking risks and prefer going for big payout sizes 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.