ISO REMCO, the ISO committee responsible for guidance on reference materials within ISO, defines the following classes of reference material:
; Reference Material:  Material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement process.
; Certified Reference Material:  Reference material characterized by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.