These terms refer to the material used to make a pot or a pan.  Materials that are reactive will cause food to taste metallic and even turn colors when they are cooked in them.  Materials that are nonreactive will not do this.  It is for this reason that some recipes make mention of the type of cooking ware or bakeware that should be used.   If you are wondering which metals are which, here is an easy to reference list: Nonreactive Bakeware Materials: • Ceramic • Enamel coated metal • Glass • Silicone • Stainless Steel Reactive Bakeware Materials: • Aluminum  • Cast iron • Copper