What is that big box around vape pens?

Question

I got a secondhand vape, I think. It's a super thin pen with a cartridge that screws into the top. I'm a newb, forgive me. I found I can use my phone charger to charge it via the USB port on the side but when I see the thing on menus, it is pictured with a big box around it. What the hell is the big box for? It works fine as it is, just a pen so...