Foot.....

The origin of the word foot, has been speculated that it was because King Henry 1st had a foot that 12inches, including is foot ware so he wanted to make the measurement of foot 12inches.

Foot is not a SI unit . Its size vary for system to system. However, the most used length is 0.30480m 304.80mm

The disadvantages of using foot as a measurement is because it is not the same from country to country unlike the matrix system.