In chemistry, a disulfide bond (Br.E. disulphide bond) is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R–S–S–R. The terminology is widely used in biochemistry. In formal terms, the connection is a persulfide, in analogy to its congener, peroxide (R–O–O–R), but this terminology is obscure and is no longer used (except in reference to R–S–S–H or H–S–S–H compounds).