Certainly, you met with the definition that a given machine has a very high variation, and this one has a medium. This is normal that at the beginning of your career such a marker will not talk to you too much. Over time, using the gaming data demo version, you will notice that they do not differ only in graphic, as well as motivations and symbols, but they also have a completely different dynamics. At this moment, we come to the concept of variability, or variance.
The slot variability can be determined as low, medium or high. In some cases, for example reviews, you will find the terms very low variability or variance high towards the average. There are players who believe such terms for unnecessary and stick to the three basic ones we described at the beginning. You, as beginners, such detailed terms can be useful. At first, however, we advise you to watch out for machines with unknown variability, because playing in can not cost you.
Some specify variability as a risk. In this case, slots with low variance are referred to as those with low risk. In the same way, when it comes to these high variance, they are called high-risk machines. These terms are coming from the fact that putting in the machine with low variability you have a better chance that part of the bet will return. In high volatility, the win will not be returned to you in every spin, but after some case you will get more than you put.