The win factor provides information about the maximum or minimum win on a spin. If the win factor is at least 0.5, this means that the smallest possible win on a spin with a Bet of 1.00 euro is 0.50 euro. If the maximum win factor is 5,000, then for a spin with a bet of 1.00 euro, this means that a maximum of 5,000 euro can be won in a "normal" game round. These example values come from the well-known Legacy of Dead slot machine. As a rule, each software Provider specifies the maximum win factor of their slot machines.
Difference between High Variance Slots and Low Variance Slots
The so-called High Variance Slots are Slot machines with the highest win factors. Consequently, players win here less often, but statistically they win a higher amount each time. An example of such a high variance slot is the popular Dead or Alive 2 slot. Here, the maximum win factor is 100,000x.
The opposite are the so-called low variance slots. Here, users win more often, but less. Usually, the maximum win factor here is 250x to 500x. So you can't generally say that a Slot machine with a higher win factor is better than a game with a low win factor. It depends on the individual needs of each Player, which slot is more suitable in each case.