About Meters (m)
A meter (if you are in America or the Philippines) or metre (the rest of the countries), is the base unit of measurement of length in the International System of Units (SI). The symbol used to express meters is m. A meter is defined as the distance travelled by light in vacuum in 1/299.792.458 of second.
The meter/metre is being used for measuring length, width and height in almost every country in the world, except in the US, where they use the Imperial/US customary units.
The meter was not always defined as the distance travelled by light in vacuum in a period of time. It was originally defined (in 1793) as one ten-millionth of the distance from the equator to the North Pole. Later, in 1799, it was redefined in terms of a prototype metre bar (which has been redefined several times). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. And finally, in 1983, the current definition was adopted (the vacuum definition).