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.

Notes: 
1) Reference material (RM) is a generic term.
2) Properties can be quantitative or qualitative, e.g. identity of substances or species.
3) Uses can include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials, and quality control.
4) An RM can only be used for a single purpose in a given measurement.