In this, participant can create categories of their own, or add concepts that are missing. It's more flexible and allows for a more accurate portrayal of a user's mental model. This approach works well for generative and exploratory work.
In this, participant is limited to using only the cards provided to them and is more likely to result in clear patterns and give an indication of which concepts relate best to which categories. This approach is better where the terminology/concepts are well established.
As the name suggests, it is a hybrid of open and closed card slot. The traditional hybrid method begins as a closed card sort but allows participants to create categories that may be missing from the card deck.