Measurement is the determination of the size or magnitude of something. Measurement is not limited to physical quantities, but can extend to quantifying almost any imaginable thing such as degree of uncertainty, consumer confidence, or the rate of increase in the fall in the price of beanie babies.
Metrology is the study of measurement.
A metric is a standard for measurement. The quantification of phenomena through the process of measurement relies on the existence of an explicit or implicit metric, which is the standard to which the measure is referenced. If I say I am '5', I am indicating a measurement without conveying an applicable standard. I may mean I am 5 years old, 5 feet high, or 5-time world raquetball champion.
For example, the unit for length might be a well-known person's foot, and the length of a boat can be given as the number of times that person's foot would fit the length of the boat.
The history of measurements is a topic within the History of Science and Technology. The meter was standardized as the unit for length after the French revolution, and has since been adopted throughout most of the world. The United States and the UK are in the process of converting to the SI system. This process is known as metrication.
Systems of measurement:physics.
Some important physical quantities include: