The process of assigning a number or category to an entity to describe an attribute of that entity.

ISO 14598 [-]

Measurement is the assignment of numbers to objects or events.

Pedhazur, Elazar J.; Schmelkin, Liora Pedhazur (1991). Measurement, Design, and Analysis: An Integrated Approach (1st ed.). Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 15–29. ISBN 0-805-81063-3. [-]