It's not like it is a universal term...
To the guy who asked the question: 'Mystery date' refers to the common but generally undesirable habit of having the back hand in front of the body/across the toe edge (like hugging a date) - this is especially counter-productive/bad form in toe-side turns.
Is this what you're talking about ? Snowboard carving technique: Extreme Carving Opus 3 - YouTube
You see this a lot in Europe and maybe Mt Hood for the race camps. Most riders today I feel dont know how to "carve", not turn but carve. Back in the day we used to compete and you competed in slalom and halfpipe, but over the years freestyle was where the money was, so slalom kinda died off (in the states), but there is still a handful of us old schoolers that enjoy carving. If you'd ever tried hardshell boots with plate binding on a race/slalom board you'd know it is a completely different style of riding and still fun to do on my All mtn boards. It gives you something to do if there's no fresh snow and killer groomers, give it a try, you might like it