https://doi.org/10.1351/goldbook.C00851
Compounds having the structure $\ce{RC(=NR)NR2}$. The term is used as a suffix in systematic nomenclature to denote the $\ce{–C(=NH)NH2}$ group including its carbon atom, e.g. acetamidine, $\ce{CH3C(=NH)NH2}$; 2-butyl-4,5-dihydroimidazole: 
