Locked Reels can work similarly to a sticky slot feature, in which an entire reel can be locked in place for the next spin that comes along. The name also implies that more than one reel can be used in play and can contain the correct symbol you wish to use on a winning combination.
Locked Reels may have appeared in a classic 3×3 slot game, where you would have a button symbol named HOLD that allows to you to lock a reel in place. That way, on the next spin, this reel will not move with the others. Other times, you may need to land a certain symbol on that reel to lock it in place or for multiples at the same time.
By using Locked Reels in a slot game, you can gain more control on how to land the symbol that you want and let you play in your own time. For example, you may want to land a symbol on a reel that is more likely to have it. This feature means that you can decide where each symbol lands where and when, like trigging the bonus symbols for the free spin round or landing the highest paying ones like a Wild symbol.
You can try and play the correct symbol you want using the Locked Reels, such as the Wild of the slot game or the Scatter. Land another Wild and you can get more combinations, or landing the Scatters and you can trigger the unique feature for that slot game. Sometimes, this isn’t 100% guaranteed though, so it is best to think wisely with which reel you want to hold and why.
Locked Reels can be added with plenty of other features to give it that unique kick, such as making the whole reel Wild, for example.