What is Ohm?

Legal Definition
The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. Although several empirically derived standard units for expressing electrical resistance were developed in connection with early telegraphy practice, the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time and of a convenient size for practical work as early as 1861. The definition of the ohm was revised several times. Today the definition of the ohm is expressed from the quantum Hall effect.
-- Wikipedia
Legal Definition
A unit for electrical resistance, the ohm which is named after the German physicist Georg Simon Ohm, is defined as the resistance between two point with a potential difference of one volt and a current flow of one ampere.