An IWeightedIngredient is an ingredient with a percentage. It is the subclass of WeightedItemStack, WeightedLiquidStack and WeightedOreDictEntry.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.item.IWeightedIngredient;

ZenGetter	What does it do	Return Type
ZenGetter ingredient	What does it do Returns the associated IIngredient	Return Type IIngredient
ZenGetter chance	What does it do Returns the stack's chance as decimal (e.g. 0.2)	Return Type float
ZenGetter percent	What does it do Returns the stack's chance as percentage (e.g. 20.0)	Return Type float