Hexavalent chromium is a general term for chromium compounds containing Cr (VI) with an oxidation number of +6. The use as a metal is common in "chrome plating" used to improve gloss, hardness, and corrosion resistance.
Hexavalent chromium compounds are extremely toxic. Although it is often used for plating purposes, the toxicity is regarded as a problem due to soil contamination. For that reason, it is no longer used as chromate treatment on zinc galvanized products in most regions with environmental regulations in place.