Short answers, pulled from the story.
The modern English word mile derives from Middle English and Old English, which was cognate with all other Germanic terms for miles. These derived from the nominal ellipsis form of 'mile' or 'miles', the Roman mile of one thousand paces.
The English statute mile was established by a Weights and Measures Act of Parliament in 1593 during the reign of Queen Elizabeth I. The applicable passage of the statute reads: A Mile shall contain eight Furlongs, every Furlong forty Poles, and every Pole shall contain sixteen Foot and half.
The international mile is precisely equal to 1609.344 meters. It was established as part of the 1959 international yard and pound agreement reached by the United States, the United Kingdom, Canada, Australia, New Zealand, and the Union of South Africa.
In October 2019, US National Geodetic Survey and National Institute of Standards and Technology announced their joint intent to retire the US survey foot and US survey mile. This was permitted by their 1959 decision with effect on the 1st of January 2023.
Since 1929 the international nautical mile is defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 meters. The Earth is not perfectly spherical but an oblate spheroid so the length of a minute of latitude increases from the equator to the poles.