A modern video slot looks simple from the outside: press a button, watch the reels, hope for a line of matching symbols. Underneath that surface sits a surprising amount of structure, and knowing how the pieces fit makes every review easier to read and every game easier to judge. None of it is secret, but most players never have it explained, so the words on a game info screen stay vaguely intimidating. Here is what is actually happening when you spin.

Two numbers follow online slots everywhere they go: return to player and volatility. They turn up in reviews, on game info screens, and in every forum argument about which title is worth a spin. The trouble is that they are usually quoted without explanation, as if everyone already agrees what they mean. They are worth understanding properly, because between them they describe almost everything about how a slot behaves, and because misreading them is the fastest way to talk yourself into expecting something a game was never built to give.