mètre

The metre, symbol m, is the base unit of length in the International System of Units (SI). It is defined as the distance light travels in vacuum in 1/299,792,458 of a second, a definition that fixes the speed of light at exactly 299,792,458 metres per second. The metre is used worldwide as the standard measure of length in science, industry, and everyday life.

The term metre comes from the French metre, which derives from the Greek metron meaning measure. Historically, the unit evolved through several definitions: in 1791 the metric system defined the metre as one ten-millionth of the distance from the equator to the North Pole along the meridian; in 1889, the international prototype metre bar made of platinum-iridium was adopted as the reference; in 1960 it was redefined in terms of the wavelength of krypton-86 light; in 1983 it was redefined again in terms of the speed of light in vacuum.

The metre has several submultiples and multipliers, including the centimeter (1/100 of a metre) and the millimeter (1/1000). It is also part of larger units like the kilometer (1000 metres). The metre remains the primary unit for measuring length in most fields, from science to engineering to everyday measurements.