Short answers, pulled from the story.
The French National Assembly defined the metre in 1791 as one ten-millionth of the distance from the equator to the North Pole along a great circle through Paris. This decision linked human measurement directly to the shape of the Earth itself.
In 1983, the International Bureau of Weights and Measures adopted a definition stating that the metre is the length of the path travelled by light in vacuum during a time interval of one second divided by 299,792,458. The definition received slight modification in 2002 to clarify it measures proper length.
The United States uses the spelling meter because the U.S. National Institute of Standards and Technology chose this form in their 2008 publication following government guidelines. The Philippines also uses meter in government and commerce despite laws using the international spelling metre.
The word metre traces its roots back to the Greek verb metron meaning I measure or count. Latin adopted the form mensura while French developed mètre before English borrowed it with first recorded usage at least as early as 1797.
One metre equals approximately 1.0936 yards or exactly 39.370 inches according to standard tables. A simple mnemonic suggests three feet plus three inches approximates one metre with minimal error.