From IVoM:

measurement unit
unit of measurement
unit
scalar quantity, defined and adopted by convention, with which any other quantity of the
same kind can be compared to express the ratio of the two quantities as a number

NOTES

1 — Measurement units are designated by conventionally assigned names and symbols.

2 — Measurement units of quantities of the same dimension may be designated by the same name and symbol even when the quantities are not of the same kind. For example joule per kelvin and J/K are respectively the name and symbol of both a measurement unit of heat capacity and a unit of entropy, which are generally not considered to be quantities of the same kind. However, in some cases special measurement unit names are restricted to be used with quantities of specific
kind only. For example, the unit 1/s is called hertz when used for frequencies and becquerel when used for activities of radionuclides.

3 — Measurement units of quantities of dimension one are numbers. In some cases these units are given special names, e.g. radian, steradian, and decibel, or are expressed by quotients such as millimole per mole equal to 10-3 and microgram per kilogram equal to 10-9.

4 — For a given quantity, the short term “unit” is often combined with the quantity name, such as “mass
unit” or “unit of mass”.

Note that a Unit is is a (scalar) Quantity, so it extends Quantity (assumed in this metamodel to be scalar).

 Visit also:

• *UnitProperty 

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