What is "ferroin"

n. (context chemistry English) A coordination compound of iron and phenanthroline used as a redox indicator

Ferroin is the chemical compound with the formula [Fe(o-phen)]SO, where o-phen is an abbreviation for 1,10- phenanthroline, a bidentate ligand. The term "ferroin" is used loosely and includes salts of other anions such as chloride.