On Cake Boss on TLC what is that flat pancake waffle thingy called they just made into tye dye to put onto the cake?

You're likely thinking of a crêpe.

Crêpes are thin, flat pancakes that are popular in French cuisine. They can be used in sweet or savory dishes and are often filled with things like fruit, whipped cream, Nutella, or savory fillings like cheese and ham.

While not a traditional method, using a crêpe to create a tie-dye effect on a cake is a creative and eye-catching way to decorate!