Ferrous metals are defined as those metals that contain iron. Non-ferrous metals do not. One of the major distinctions in specialization is whether foundries work with ferrous metals, non-ferrous metals, or both. The definition of a ferrous metal is any metal that contains iron; non-ferrous metals do not.
When a metal is defined as non-ferrous it means that it does not have a significant amount of iron in its chemical composition. Note the word “significant”; nearly all metal alloys have some trace, or non-significant, amount of iron in their composition. This does not make them ferrous alloys though.