The stuff on a shuffleboard table is shuffleboard wax- also known as dust, sand, cheese, powder, salt, and sawdust. It’s primarily made of cornmeal and silicone.
It is non-toxic and not at all dangerous, and is sprinkled onto shuffleboards for three primary reasons.
Firstly, it serves to decrease friction between the puck and the table. Secondly, it preserves the table’s thickness, and thirdly it increases the speed of weights as they glide across the table. Overall, shuffleboard wax preserves the quality and precision of your table and your play, allowing your puck to glide smoother and easier.