What does «metro» mean in Spanish?
- This article is about the meter (unit). For other uses of the term "meter", please see "meter" (disambiguation). The meter (American meter) is the basic unit of measurement of length in the International System of Units (SI), commonly known as the metric system. The meter is abbreviated as m, which appears after the quantity. The meter has been adopted as the fundamental unit of length in almost every country in the world, with the notable exception of the United States. Currently, SI units define the meter in terms of the speed of light and the second, such that the meter is the length traveled by light in the reference medium of classical vacuum in the time interval 1/299 792 458 seconds. An easy to perform and reproducible measurement is one of the main objectives of metrology. The feasibility of adopting time of flight as a measure of length depends primarily on the experimental fact that the speed of light in vacuum is a universal constant within experimental error. Its practicality is reinforced by the fact that the corrections introduced by using real media, such as terrestrial vacuum, or even air, are very small.