Some Microgaming bonus slots have some unique rules including a gamble option, the ability to re-spin the reels, to nudge the reels and to hold the reels. The option of holding the reels will happen after you have spun the reels the first time. At random intervals you will be able to re-spin the reels for free, but keep some or all of reels still. This helps you line up that final third reel much more easily and it is also a free bonus.

Here we decided to hold the middle reel while we use our free re-spin.
Here we won six times our initial wager because of the re-spin.