What is difference between one hot encoding and leave one out encoding?
They are probably using &quot;leave one out encoding&quot; to refer to Owen Zhang's strategy.
From here
The encoded column is not a conventional dummy variable, but instead is the mean response over all rows for this categorical level, excluding the row itself. This gives you the advantage of having a one-column representation of the categorical while avoiding direct response leakage
This picture expresses the idea well.