Deposit £20 at a UKGC-licensed casino and open a slot you have never tried. Ten spins later the balance reads £14. The next twenty spins give two small wins, and the balance sits at £32. On spin 38 a feature arrives, and the balance jumps to £61. A run of silent reels followed by a sudden climb is not a fault in the machine. The game has a volatility profile, and that profile decides when the wins turn up and when they stay away.
Volatility holds two measurements together: how often a slot pays and how large one of those prizes can be. A low-volatility game gives out small wins on a steady beat, so the balance rolls along in gentle steps. A high-volatility game passes through long empty stretches and then produces a handful of larger wins. Two titles can show the same return to player and still feel nothing alike, because RTP describes a very long average. The ride between the start and that average is the volatility, and the ride is the only part a player actually occupies.
If you want to understand volatility distribution completely, read what slot volatility means before you choose a game. The label low, medium or high maps directly onto the frequency and size of payouts.
A cold run is a normal part of high-variance play, and learning the cold side of slot volatility can stop you from chasing losses.
Book of Dead shows exactly how a high-volatility slot behaves between empty spins and the occasional large feature.
This is why slot volatility outranks RTP for any short real-money session: RTP averages over millions of spins, while variance defines the next few hours.
Volatility should also affect how you use your bonus. Check the wagering legs, and use the clear example of the Lucky Lion Bonus as a guide before you deposit. Set a bankroll, choose the right volatility, and play.