Variance is the spread of actual results around the expected average. Put simply, it shows how far real outcomes can swing up or down over a short stretch.

How does it work?

In betting and casino play, you can make perfectly reasonable decisions and still hit a rough downswing. Or you can catch a very lucky run. That is what variance describes. In slots, it is often tied to how rarely the game pays large wins. In betting, it reflects how long results can run against expectation, even when the overall approach is solid.