From Elsmar Cove Quality Assurance and Business Standards Wiki
Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. Measurement usually involves using a measuring instrument, which is calibrated to compare the object to some standard.
Like any process, measurement involves the interaction of people, methods, materials, and equipment in an environment to produce an output in this case a number or evaluation. To extract meaning from measurements, the measurement process must be stable (in statistical control).
See also
Related Elsmar Cove Forum Measurement Feedback Discussion Threads
References
Wikipedia article on Measurement