The phrase "empty pod" refers to something that is vacant or has nothing inside it. It can describe a place or object that is completely devoid of anything or anyone. Full definition
Scrape out the seeds of the vanilla bean into the mixture and toss in the empty pod. (spachethespatula.com)
And every once in a while, when you're using a fresh bean in a recipe, you can add the empty pod (rinsed off and dried if it's been steeped in milk or cream) to the jar (see note). (cnz.to)
Add in the milk, coconut cream, sugar, vanilla bean seeds and empty pod, nutmeg, and dates. (spachethespatula.com)