The ohm (symbol: O) 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.

OHM (sometimes stylized Ohm: or OHM:) is an American instrumental rock/jazz fusion group fronted by former Megadeth guitarist Chris Poland. The band was formed in 2002 and has released three studio albums and a live album. A similar offshoot band named OHMphrey, also fronted by Poland, was formed in 2008.

Ohm (O) refers to the SI unit of electrical resistance named after Georg Ohm.