... doesn’t exist!
Well okay – if you read my last piece this was no surprise after the title, I guess...
There are definitions of planning poker like the ones on wikipedia or the popular description from mountain goat – But you won‘t find planning poker in the original Scrum resources. Neither in the book, nor in the paper, and not the Scrum guide.
You also might want to reconsider if you really need planning poker for your estimation. There is a lot of thought about not needing estimation at all (not freeing one from the need for analysis, though!) and there are other options like magic estimation (sometimes also called affinity estimation)
till next time