Standard solution:

A solution of accurately known concentration, prepared using standard
substances in one of several ways. A primary standard is a substance of
known high purity which may be dissolved in a known volume of solvent
to give a primary standard solution. If stoichiometry is used to establish
the strength of a titrant, it is called a secondary standard solution. The term
secondary standard can also be applied to a substance whose active agent
contents have been found by comparison against a primary standard. Concentrations
of standard solutions may be expressed in kmol m^–3, mol dm^–3,
or in terms more closely related to those used in specific titrations (as titres).

O.B. 48 IUPAC Compendium of Chemical Terminology 2nd Edition (1997)