TPD Version

I'm a bit confused, I have been trying to find out what this means. I'm purchasing the Aspire Nautilus AIO and some extra coils from the site and in the drop down menu it says TPD Version. I can't seem to find clarification to what this actually means or entails and I would like to do so before make the purchase final. Thanks in advance to anyone who can explain this or provide some closure on my confusion.

The Lady Amelia
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