Według słownika.

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Note added at 10 mins (2015-04-28 20:21:09 GMT)
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Early boots consisted of separate leggings, soles, and uppers worn together to provide greater ankle protection than shoes[1] or sandals. Around 1000 BC, these components were more permanently joined to form a single unit that covered the feet and lower leg, often up to the knee. (...) Waterproof gumboots are made in different lengths of uppers.
https://en.wikipedia.org/wiki/Boot

The shaft of a boot refers to the portion of the boot that rises above your foot and over your calf. - http://www.wikihow.com/Measure-Boot-Shaft

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Shaft - The height of the shaft measured from the middle of the arch up the outsole of the boot to the top of the boot shaft in inches. - http://www.zappos.com/measurement-guide