It's an accordion and it's there because you are using this app https://apps.shopify.com/product-description-accordion
I deleted the app from my store a few days ago, do you know how to make it not apply anymore? Its doesn't show up when I go to my apps.
Looks like you worked it out, as it's working now. The app must have left some of its code behind when you deleted it. If you haven't done much customization to your theme yet it might be worth downloading a clean version of Debut and using that instead or try and find the leftover code in your existing theme and remove it.