Feedstock: Semi useful things made from the raw materials, such as Chlorine.
BiProduct: Something you accidentally made.
CoProduct: Something you accidentally made, but is useful.
Rutile Ore, Rock salt and water ----> Titanium(IV)Oxide, Chlorine and Water ---->Titanium Oxide.
The Rutile Ore, the rock salt and the water are Raw Material/Feedstock. Because it's the input.
Titanium(IV)Oxide is the product. Because it's what you wanted.
Chlorine is the CoProduct. Because it's not what you wanted, but you can still use it for something else.