Imagine you have a cookie, but instead of being a round and delicious treat, it's been turned into small pieces of crumbly dough. That's what we call ground biscuit! It's the result of taking a bunch of cookies and crushing them into tiny bits.
This can be done using special machines or tools, kind of like a blender or food processor, but bigger and more industrial-grade. The crumbs might be used to make other tasty treats, like pie crust or as a topping for ice cream.
So basically, ground biscuit is just smashed-up cookies that have been turned into small pieces, ready to be used in other recipes. Yum!