What is imperial unit?

Answer 1

Imperial units or the imperial system is a system of units, first defined in the British Weights and Measures Act of 1824, later refined (until 1959) and reduced. Systems of imperial units are sometimes referred to as foot-pound-second, after the base units of length, mass and time. The units were introduced in the British Empire, excluding the then already independent United States. As of 2008, all countries that used the imperial system have become officially metric, except for the United States, Burma and Liberia, however some other countries have laws mandating or permitting other systems of measurement, such as the United Kingdomwhich still uses many imperial measures, such as miles and yards for road signs, lb/oz, pints, etc. for many products, and also uses inches and barleycorns for clothing and shoe sizes respectively.

according to http://en.wikipedia.org