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