Variance and volatility are two words for how widely results spread around the expected outcome, used interchangeably in gambling.
Volatility decides how long a bankroll is likely to last and how a session feels, even when two games return the same amount over time.
Two slots can both run at 96 percent RTP. A low volatility game pays small amounts often. A high volatility game pays rarely and large. The long-run return is the same and the experience is completely different.
Usually not. High volatility games have long losing runs, so a small bankroll is more likely to run out before a large win lands.
Many game information panels show a volatility rating set by the studio. It is a descriptive band rather than a regulated figure.