Ferrous (Fe2+), in chemistry, indicates a divalent iron compound (+2 oxidation state), as opposed to ferric, which indicates a trivalent iron compound (+3 oxidation state). This usage has mostly been deprecated, with current IUPAC nonclemature with names containing the oxidation state in bracketed roman numerals instead, such as iron (III) oxide for Fe2O3.
Outside of chemistry, ferrous is an adjective used to indicate the presence of iron. The word is derived from the Latin word ferrum ("iron"). Ferrous metals include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel).
The term non-ferrous is used to indicate metals other than iron and alloys that do not contain an appreciable amount of iron.